From 0759e170a7faafca0cee7b9b8929b0c6e15bcf77 Mon Sep 17 00:00:00 2001
From: vbuterin <v@buterin.com>
Date: Thu, 7 Mar 2019 01:38:03 -0600
Subject: [PATCH 01/17] High/low balance separation

See #685 for reasoning
---
 specs/core/0_beacon-chain.md | 95 +++++++++++++++++++++++++++---------
 1 file changed, 72 insertions(+), 23 deletions(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index bd709218a..3c2d90b69 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -64,6 +64,10 @@
         - [`get_epoch_start_slot`](#get_epoch_start_slot)
         - [`is_active_validator`](#is_active_validator)
         - [`get_active_validator_indices`](#get_active_validator_indices)
+        - [`get_balance`](#get_balance)
+        - [`set_balance`](#set_balance)
+        - [`increase_balance`](#increase_balance)
+        - [`decrease_balance`](#decrease_balance)
         - [`get_permuted_index`](#get_permuted_index)
         - [`split`](#split)
         - [`get_epoch_committee_count`](#get_epoch_committee_count)
@@ -205,10 +209,10 @@ Code snippets appearing in `this style` are to be interpreted as Python code.
 
 | Name | Value | Unit |
 | - | - | :-: |
-| `MIN_DEPOSIT_AMOUNT` | `2**0 * 10**9` (= 1,000,000,000) | Gwei |
+| `MIN_DEPOSIT_AMOUNT` | `2**0 * 10**9` (= 2,000,000,000) | Gwei |
 | `MAX_DEPOSIT_AMOUNT` | `2**5 * 10**9` (= 32,000,000,000) | Gwei |
-| `FORK_CHOICE_BALANCE_INCREMENT` | `2**0 * 10**9` (= 1,000,000,000) | Gwei |
 | `EJECTION_BALANCE` | `2**4 * 10**9` (= 16,000,000,000) | Gwei |
+| `HIGH_BALANCE_INCREMENT` | `10 ** 9` (= 1,000,000,000) | Gwei |
 
 ### Initial values
 
@@ -516,7 +520,7 @@ The following data structures are defined as [SimpleSerialize (SSZ)](https://git
 
     # Validator registry
     'validator_registry': [Validator],
-    'validator_balances': ['uint64'],
+    'low_balances': ['uint32'],
     'validator_registry_update_epoch': 'uint64',
 
     # Randomness and committees
@@ -570,6 +574,8 @@ The following data structures are defined as [SimpleSerialize (SSZ)](https://git
     'initiated_exit': 'bool',
     # Was the validator slashed
     'slashed': 'bool',
+    # Rounded balance
+    'high_balance': 'uint32'
 }
 ```
 
@@ -749,6 +755,45 @@ def get_active_validator_indices(validators: List[Validator], epoch: Epoch) -> L
     return [i for i, v in enumerate(validators) if is_active_validator(v, epoch)]
 ```
 
+### `get_balance`
+
+```python
+def get_balance(state: BeaconState, index: int) -> int:
+    return (
+        state.validator_registry[index].high_balance * HIGH_BALANCE_INCREMENT + 
+        state.low_balances[index]
+    )
+```
+#### `set_balance`
+
+````python
+def set_balance(state: BeaconState, index: int, new_balance: int) -> None:
+    validator = state.validator_registry[index]
+    HALF_INCREMENT = HIGH_BALANCE_INCREMENT // 2
+    if (
+        validator.rounded_balance * HIGH_BALANCE_INCREMENT > new_balance or
+        validator.rounded_balance * HIGH_BALANCE_INCREMENT + HALF_INCREMENT * 3 < new_balance
+    ):
+        validator.rounded_balance = new_balance // HIGH_BALANCE_INCREMENT
+    state.validator_fractional_balances[index] = (
+        new_balance - validator.rounded_balance * HIGH_BALANCE_INCREMENT
+    )
+````
+
+#### `increase_balance`
+
+````python
+def increase_balance(state: BeaconState, index: int, delta: int) -> None:
+    set_balance(state, index, get_balance(state, index) + delta)
+````
+
+#### `decrease_balance`
+
+````python
+def decrease_balance(state: BeaconState, index: int, delta: int) -> None:
+    set_balance(state, index, get_balance(state, index) - delta)
+````
+
 ### `get_permuted_index`
 
 ```python
@@ -1105,7 +1150,7 @@ def get_effective_balance(state: BeaconState, index: ValidatorIndex) -> Gwei:
     """
     Return the effective balance (also known as "balance at stake") for a validator with the given ``index``.
     """
-    return min(state.validator_balances[index], MAX_DEPOSIT_AMOUNT)
+    return min(get_balance(state, index), MAX_DEPOSIT_AMOUNT)
 ```
 
 ### `get_total_balance`
@@ -1351,17 +1396,18 @@ def process_deposit(state: BeaconState, deposit: Deposit) -> None:
             withdrawable_epoch=FAR_FUTURE_EPOCH,
             initiated_exit=False,
             slashed=False,
+            high_balance=0
         )
 
         # Note: In phase 2 registry indices that have been withdrawn for a long time will be recycled.
         state.validator_registry.append(validator)
-        state.validator_balances.append(amount)
+        state.low_balances.append(0)
+        set_balance(state, len(state.validator_registry)-1, amount)
     else:
         # Increase balance by deposit amount
         index = validator_pubkeys.index(pubkey)
         assert state.validator_registry[index].withdrawal_credentials == withdrawal_credentials
-
-        state.validator_balances[index] += amount
+        increase_balance(state, index, amount)
 ```
 
 ### Routines for updating validator status
@@ -1426,8 +1472,8 @@ def slash_validator(state: BeaconState, index: ValidatorIndex) -> None:
 
     whistleblower_index = get_beacon_proposer_index(state, state.slot)
     whistleblower_reward = get_effective_balance(state, index) // WHISTLEBLOWER_REWARD_QUOTIENT
-    state.validator_balances[whistleblower_index] += whistleblower_reward
-    state.validator_balances[index] -= whistleblower_reward
+    increase_balance(state, whistleblower_index, whistleblower_reward)
+    decrease_balance(state, index, whistleblower_reward)
     validator.slashed = True
     validator.withdrawable_epoch = get_current_epoch(state) + LATEST_SLASHED_EXIT_LENGTH 
 ```
@@ -1545,7 +1591,7 @@ def get_genesis_beacon_state(genesis_validator_deposits: List[Deposit],
 
         # Validator registry
         validator_registry=[],
-        validator_balances=[],
+        low_balances=[],
         validator_registry_update_epoch=GENESIS_EPOCH,
 
         # Randomness and committees
@@ -1657,9 +1703,12 @@ def lmd_ghost(store: Store, start_state: BeaconState, start_block: BeaconBlock)
         for validator_index in active_validator_indices
     ]
 
+    # Use the rounded-balance-with-hysteresis supplied by the protocol for fork
+    # choice voting. This reduces the number of recomputations that need to be
+    # made for optimized implementations that precompute and save data
     def get_vote_count(block: BeaconBlock) -> int:
         return sum(
-            get_effective_balance(start_state.validator_balances[validator_index]) // FORK_CHOICE_BALANCE_INCREMENT
+            start_state.validator_registry[validator_index].high_balance
             for validator_index, target in attestation_targets
             if get_ancestor(store, target, block.slot) == block
         )
@@ -1956,12 +2005,12 @@ def process_transfer(state: BeaconState, transfer: Transfer) -> None:
     Note that this function mutates ``state``.
     """
     # Verify the amount and fee aren't individually too big (for anti-overflow purposes)
-    assert state.validator_balances[transfer.sender] >= max(transfer.amount, transfer.fee)
+    assert get_balance(state, transfer.sender) >= max(transfer.amount, transfer.fee)
     # Verify that we have enough ETH to send, and that after the transfer the balance will be either
     # exactly zero or at least MIN_DEPOSIT_AMOUNT
     assert (
-        state.validator_balances[transfer.sender] == transfer.amount + transfer.fee or
-        state.validator_balances[transfer.sender] >= transfer.amount + transfer.fee + MIN_DEPOSIT_AMOUNT
+        get_balance(state, transfer.sender) == transfer.amount + transfer.fee or
+        get_balance(state, transfer.sender) >= transfer.amount + transfer.fee + MIN_DEPOSIT_AMOUNT
     )
     # A transfer is valid in only one slot
     assert state.slot == transfer.slot
@@ -1983,9 +2032,9 @@ def process_transfer(state: BeaconState, transfer: Transfer) -> None:
         domain=get_domain(state.fork, slot_to_epoch(transfer.slot), DOMAIN_TRANSFER)
     )
     # Process the transfer
-    state.validator_balances[transfer.sender] -= transfer.amount + transfer.fee
-    state.validator_balances[transfer.recipient] += transfer.amount
-    state.validator_balances[get_beacon_proposer_index(state, state.slot)] += transfer.fee
+    decrease_balance(state, transfer.sender, transfer.amount + transfer.fee)
+    increase_balance(state, transfer.recipient, transfer.amount)
+    increase_balance(state, get_beacon_proposer_index(state, state.slot), transfer.fee)
 ```
 
 ### Per-epoch processing
@@ -2320,10 +2369,10 @@ def apply_rewards(state: BeaconState) -> None:
     deltas1 = get_justification_and_finalization_deltas(state)
     deltas2 = get_crosslink_deltas(state)
     for i in range(len(state.validator_registry)):
-        state.validator_balances[i] = max(
+        set_balance(state, i, max(
             0,
-            state.validator_balances[i] + deltas1[0][i] + deltas2[0][i] - deltas1[1][i] - deltas2[1][i]
-        )
+            get_balance(state, i) + deltas1[0][i] + deltas2[0][i] - deltas1[1][i] - deltas2[1][i]
+        ))
 ```
 
 #### Ejections
@@ -2337,7 +2386,7 @@ def process_ejections(state: BeaconState) -> None:
     and eject active validators with balance below ``EJECTION_BALANCE``.
     """
     for index in get_active_validator_indices(state.validator_registry, get_current_epoch(state)):
-        if state.validator_balances[index] < EJECTION_BALANCE:
+        if get_balance(state, index) < EJECTION_BALANCE:
             exit_validator(state, index)
 ```
 
@@ -2380,7 +2429,7 @@ def update_validator_registry(state: BeaconState) -> None:
     # Activate validators within the allowable balance churn
     balance_churn = 0
     for index, validator in enumerate(state.validator_registry):
-        if validator.activation_epoch == FAR_FUTURE_EPOCH and state.validator_balances[index] >= MAX_DEPOSIT_AMOUNT:
+        if validator.activation_epoch == FAR_FUTURE_EPOCH and get_balance(state, index) >= MAX_DEPOSIT_AMOUNT:
             # Check the balance churn would be within the allowance
             balance_churn += get_effective_balance(state, index)
             if balance_churn > max_balance_churn:
@@ -2461,7 +2510,7 @@ def process_slashings(state: BeaconState) -> None:
                 get_effective_balance(state, index) * min(total_penalties * 3, total_balance) // total_balance,
                 get_effective_balance(state, index) // MIN_PENALTY_QUOTIENT
             )
-            state.validator_balances[index] -= penalty
+            decrease_balance(state, index, penalty)
 ```
 
 ```python

From be4b912373b9ee89851e217e8f500f444ef0e1fa Mon Sep 17 00:00:00 2001
From: vbuterin <v@buterin.com>
Date: Thu, 7 Mar 2019 04:02:53 -0600
Subject: [PATCH 02/17] Added underflow checking to decrease_balance

---
 specs/core/0_beacon-chain.md | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 3c2d90b69..b0b3dbb2a 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -791,7 +791,8 @@ def increase_balance(state: BeaconState, index: int, delta: int) -> None:
 
 ````python
 def decrease_balance(state: BeaconState, index: int, delta: int) -> None:
-    set_balance(state, index, get_balance(state, index) - delta)
+    cur_balance = get_balance(state, index)
+    set_balance(state, index, cur_balance - delta if cur_balance >= delta else 0)
 ````
 
 ### `get_permuted_index`

From f9a07f7653890fd74c6c023182ccb56004b5579d Mon Sep 17 00:00:00 2001
From: vbuterin <v@buterin.com>
Date: Thu, 7 Mar 2019 04:04:05 -0600
Subject: [PATCH 03/17] Fixed MIN_DEPOSIT_AMOUNT

---
 specs/core/0_beacon-chain.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index b0b3dbb2a..c548dbe14 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -209,10 +209,10 @@ Code snippets appearing in `this style` are to be interpreted as Python code.
 
 | Name | Value | Unit |
 | - | - | :-: |
-| `MIN_DEPOSIT_AMOUNT` | `2**0 * 10**9` (= 2,000,000,000) | Gwei |
+| `MIN_DEPOSIT_AMOUNT` | `10**9` (= 1,000,000,000) | Gwei |
 | `MAX_DEPOSIT_AMOUNT` | `2**5 * 10**9` (= 32,000,000,000) | Gwei |
 | `EJECTION_BALANCE` | `2**4 * 10**9` (= 16,000,000,000) | Gwei |
-| `HIGH_BALANCE_INCREMENT` | `10 ** 9` (= 1,000,000,000) | Gwei |
+| `HIGH_BALANCE_INCREMENT` | `10**9` (= 1,000,000,000) | Gwei |
 
 ### Initial values
 

From bf6bdbb0210ee8020cac21b3f731178caad03ab7 Mon Sep 17 00:00:00 2001
From: Danny Ryan <dannyjryan@gmail.com>
Date: Mon, 11 Mar 2019 12:38:11 -0600
Subject: [PATCH 04/17] cleanup minor var errors

---
 specs/core/0_beacon-chain.md | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index f5fa2128a..ec9eedb51 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -768,12 +768,12 @@ def set_balance(state: BeaconState, index: int, new_balance: int) -> None:
     validator = state.validator_registry[index]
     HALF_INCREMENT = HIGH_BALANCE_INCREMENT // 2
     if (
-        validator.rounded_balance * HIGH_BALANCE_INCREMENT > new_balance or
-        validator.rounded_balance * HIGH_BALANCE_INCREMENT + HALF_INCREMENT * 3 < new_balance
+        validator.high_balance * HIGH_BALANCE_INCREMENT > new_balance or
+        validator.high_balance * HIGH_BALANCE_INCREMENT + HALF_INCREMENT * 3 < new_balance
     ):
-        validator.rounded_balance = new_balance // HIGH_BALANCE_INCREMENT
-    state.validator_fractional_balances[index] = (
-        new_balance - validator.rounded_balance * HIGH_BALANCE_INCREMENT
+        validator.high_balance = new_balance // HIGH_BALANCE_INCREMENT
+    state.low_balances[index] = (
+        new_balance - validator.high_balance * HIGH_BALANCE_INCREMENT
     )
 ````
 

From a7544864d5de8eaa27f4630d2740f4acc8383d99 Mon Sep 17 00:00:00 2001
From: Justin <drakefjustin@gmail.com>
Date: Tue, 12 Mar 2019 10:02:52 +0000
Subject: [PATCH 05/17] Update 0_beacon-chain.md

---
 specs/core/0_beacon-chain.md | 24 ++++++++----------------
 1 file changed, 8 insertions(+), 16 deletions(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index ec9eedb51..7d59a9e6d 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -203,10 +203,10 @@ Code snippets appearing in `this style` are to be interpreted as Python code.
 
 | Name | Value | Unit |
 | - | - | :-: |
-| `MIN_DEPOSIT_AMOUNT` | `10**9` (= 1,000,000,000) | Gwei |
+| `MIN_DEPOSIT_AMOUNT` | `2**0 * 10**9` (= 1,000,000,000) | Gwei |
 | `MAX_DEPOSIT_AMOUNT` | `2**5 * 10**9` (= 32,000,000,000) | Gwei |
 | `EJECTION_BALANCE` | `2**4 * 10**9` (= 16,000,000,000) | Gwei |
-| `HIGH_BALANCE_INCREMENT` | `10**9` (= 1,000,000,000) | Gwei |
+| `HIGH_BALANCE_INCREMENT` | `2**0 * 10**9` (= 1,000,000,000) | Gwei |
 
 ### Initial values
 
@@ -440,7 +440,7 @@ The types are defined topologically to aid in facilitating an executable version
     # Was the validator slashed
     'slashed': 'bool',
     # Rounded balance
-    'high_balance': 'uint32'
+    'high_balance': 'uint64'
 }
 ```
 
@@ -756,25 +756,17 @@ def get_active_validator_indices(validators: List[Validator], epoch: Epoch) -> L
 
 ```python
 def get_balance(state: BeaconState, index: int) -> int:
-    return (
-        state.validator_registry[index].high_balance * HIGH_BALANCE_INCREMENT + 
-        state.low_balances[index]
-    )
+    return state.validator_registry[index].high_balance + state.low_balances[index]
 ```
 #### `set_balance`
 
 ````python
-def set_balance(state: BeaconState, index: int, new_balance: int) -> None:
+def set_balance(state: BeaconState, index: int, balance: int) -> None:
     validator = state.validator_registry[index]
     HALF_INCREMENT = HIGH_BALANCE_INCREMENT // 2
-    if (
-        validator.high_balance * HIGH_BALANCE_INCREMENT > new_balance or
-        validator.high_balance * HIGH_BALANCE_INCREMENT + HALF_INCREMENT * 3 < new_balance
-    ):
-        validator.high_balance = new_balance // HIGH_BALANCE_INCREMENT
-    state.low_balances[index] = (
-        new_balance - validator.high_balance * HIGH_BALANCE_INCREMENT
-    )
+    if validator.high_balance > balance or validator.high_balance + 3 * HALF_INCREMENT < balance:
+        validator.high_balance = balance - balance % HIGH_BALANCE_INCREMENT
+    state.low_balances[index] = balance - validator.high_balance
 ````
 
 #### `increase_balance`

From 0a349f8bdc31d08f2c6f4a5b8e98427845c1716e Mon Sep 17 00:00:00 2001
From: Justin <drakefjustin@gmail.com>
Date: Tue, 12 Mar 2019 15:58:31 +0000
Subject: [PATCH 06/17] Update 0_beacon-chain.md

---
 specs/core/0_beacon-chain.md | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 7d59a9e6d..63737962d 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -601,7 +601,7 @@ The types are defined topologically to aid in facilitating an executable version
 
     # Validator registry
     'validator_registry': [Validator],
-    'low_balances': ['uint32'],
+    'balances': ['uint64'],
     'validator_registry_update_epoch': 'uint64',
 
     # Randomness and committees
@@ -756,7 +756,7 @@ def get_active_validator_indices(validators: List[Validator], epoch: Epoch) -> L
 
 ```python
 def get_balance(state: BeaconState, index: int) -> int:
-    return state.validator_registry[index].high_balance + state.low_balances[index]
+    return state.balances[index]
 ```
 #### `set_balance`
 
@@ -766,7 +766,7 @@ def set_balance(state: BeaconState, index: int, balance: int) -> None:
     HALF_INCREMENT = HIGH_BALANCE_INCREMENT // 2
     if validator.high_balance > balance or validator.high_balance + 3 * HALF_INCREMENT < balance:
         validator.high_balance = balance - balance % HIGH_BALANCE_INCREMENT
-    state.low_balances[index] = balance - validator.high_balance
+    state.balances[index] = balance
 ````
 
 #### `increase_balance`
@@ -1377,7 +1377,7 @@ def process_deposit(state: BeaconState, deposit: Deposit) -> None:
 
         # Note: In phase 2 registry indices that have been withdrawn for a long time will be recycled.
         state.validator_registry.append(validator)
-        state.low_balances.append(0)
+        state.balances.append(0)
         set_balance(state, len(state.validator_registry)-1, amount)
     else:
         # Increase balance by deposit amount
@@ -1567,7 +1567,7 @@ def get_genesis_beacon_state(genesis_validator_deposits: List[Deposit],
 
         # Validator registry
         validator_registry=[],
-        low_balances=[],
+        balances=[],
         validator_registry_update_epoch=GENESIS_EPOCH,
 
         # Randomness and committees

From dc4b652f72339063bfbaae378e850d173168c9f6 Mon Sep 17 00:00:00 2001
From: Justin <drakefjustin@gmail.com>
Date: Tue, 19 Mar 2019 11:03:42 +0000
Subject: [PATCH 07/17] Only slash active validators

This is to prevent a spam/DoS attack where validators with zero balance get "slashed" but no validator loses any balance.
---
 specs/core/0_beacon-chain.md | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index a631bf2fc..2113472e3 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -2315,8 +2315,8 @@ def process_proposer_slashing(state: BeaconState,
     assert slot_to_epoch(proposer_slashing.header_1.slot) == slot_to_epoch(proposer_slashing.header_2.slot)
     # But the headers are different
     assert proposer_slashing.header_1 != proposer_slashing.header_2
-    # Proposer is not yet slashed
-    assert proposer.slashed is False
+    # Proposer is active and not already slashed
+    assert is_active_validator(proposer) and proposer.slashed is False
     # Signatures are valid
     for header in (proposer_slashing.header_1, proposer_slashing.header_2):
         assert bls_verify(
@@ -2355,6 +2355,7 @@ def process_attester_slashing(state: BeaconState,
         index for index in attestation1.validator_indices
         if (
             index in attestation2.validator_indices and
+            is_active_validator(state.validator_registry[index]) and
             state.validator_registry[index].slashed is False
         )
     ]

From 2b454d57f11d8e1bde78dd1aa83116df2b2417ee Mon Sep 17 00:00:00 2001
From: Justin <drakefjustin@gmail.com>
Date: Tue, 19 Mar 2019 11:08:17 +0000
Subject: [PATCH 08/17] Update 0_beacon-chain.md

---
 specs/core/0_beacon-chain.md | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 2113472e3..9ed620b83 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -59,6 +59,7 @@
         - [`get_current_epoch`](#get_current_epoch)
         - [`get_epoch_start_slot`](#get_epoch_start_slot)
         - [`is_active_validator`](#is_active_validator)
+        - [`is_slashable_validator`](#is_slashable_validator)
         - [`get_active_validator_indices`](#get_active_validator_indices)
         - [`get_permuted_index`](#get_permuted_index)
         - [`split`](#split)
@@ -737,6 +738,18 @@ def is_active_validator(validator: Validator, epoch: Epoch) -> bool:
     return validator.activation_epoch <= epoch < validator.exit_epoch
 ```
 
+### `is_slashable_validator`
+```python
+def is_slashable_validator(validator: Validator, epoch: Epoch) -> bool:
+    """
+    Check if ``validator`` is slashable.
+    """
+    return (
+        validator.activation_epoch <= epoch < validator.withdrawable_epoch and
+        validator.slashed is False
+    )
+```
+
 ### `get_active_validator_indices`
 
 ```python
@@ -2315,8 +2328,8 @@ def process_proposer_slashing(state: BeaconState,
     assert slot_to_epoch(proposer_slashing.header_1.slot) == slot_to_epoch(proposer_slashing.header_2.slot)
     # But the headers are different
     assert proposer_slashing.header_1 != proposer_slashing.header_2
-    # Proposer is active and not already slashed
-    assert is_active_validator(proposer) and proposer.slashed is False
+    # Check proposer is slashable
+    assert is_slashable_validator(proposer)
     # Signatures are valid
     for header in (proposer_slashing.header_1, proposer_slashing.header_2):
         assert bls_verify(
@@ -2355,8 +2368,7 @@ def process_attester_slashing(state: BeaconState,
         index for index in attestation1.validator_indices
         if (
             index in attestation2.validator_indices and
-            is_active_validator(state.validator_registry[index]) and
-            state.validator_registry[index].slashed is False
+            is_slashable_validator(state.validator_registry[index])
         )
     ]
     assert len(slashable_indices) >= 1

From 0c383ce4a1d4770bdb21975023a2ca7a3ef5f522 Mon Sep 17 00:00:00 2001
From: Justin <drakefjustin@gmail.com>
Date: Tue, 19 Mar 2019 11:11:18 +0000
Subject: [PATCH 09/17] Update 0_beacon-chain.md

---
 specs/core/0_beacon-chain.md | 1 -
 1 file changed, 1 deletion(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 9ed620b83..d377b8d45 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -1412,7 +1412,6 @@ def slash_validator(state: BeaconState, index: ValidatorIndex) -> None:
     Note that this function mutates ``state``.
     """
     validator = state.validator_registry[index]
-    assert state.slot < get_epoch_start_slot(validator.withdrawable_epoch)  # [TO BE REMOVED IN PHASE 2]
     exit_validator(state, index)
     state.latest_slashed_balances[get_current_epoch(state) % LATEST_SLASHED_EXIT_LENGTH] += get_effective_balance(state, index)
 

From e91036cfc9fbf9d05b03da0180ed5be95cc916ca Mon Sep 17 00:00:00 2001
From: Justin <drakefjustin@gmail.com>
Date: Tue, 19 Mar 2019 11:12:50 +0000
Subject: [PATCH 10/17] Update 0_beacon-chain.md

---
 specs/core/0_beacon-chain.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index d377b8d45..4a6170418 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -2328,7 +2328,7 @@ def process_proposer_slashing(state: BeaconState,
     # But the headers are different
     assert proposer_slashing.header_1 != proposer_slashing.header_2
     # Check proposer is slashable
-    assert is_slashable_validator(proposer)
+    assert is_slashable_validator(proposer, get_current_epoch(state))
     # Signatures are valid
     for header in (proposer_slashing.header_1, proposer_slashing.header_2):
         assert bls_verify(
@@ -2367,7 +2367,7 @@ def process_attester_slashing(state: BeaconState,
         index for index in attestation1.validator_indices
         if (
             index in attestation2.validator_indices and
-            is_slashable_validator(state.validator_registry[index])
+            is_slashable_validator(state.validator_registry[index], get_current_epoch(state))
         )
     ]
     assert len(slashable_indices) >= 1

From 833691b8afe9ca68c75588e0f528780f200de0ee Mon Sep 17 00:00:00 2001
From: Justin <drakefjustin@gmail.com>
Date: Wed, 20 Mar 2019 08:16:39 +0000
Subject: [PATCH 11/17] Update 0_beacon-chain.md

---
 specs/core/0_beacon-chain.md | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 4935ab7d7..099d12b95 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -256,7 +256,7 @@ Code snippets appearing in `this style` are to be interpreted as Python code.
 | `MIN_PENALTY_QUOTIENT` | `2**5` (= 32) |
 
 * The `BASE_REWARD_QUOTIENT` parameter dictates the per-epoch reward. It corresponds to ~2.54% annual interest assuming 10 million participating ETH in every epoch.
-* The `INACTIVITY_PENALTY_QUOTIENT` equals `INVERSE_SQRT_E_DROP_TIME**2` where `INVERSE_SQRT_E_DROP_TIME := 2**12 epochs` (~18 days) is the time it takes the inactivity penalty to reduce the balance of non-participating [validators](#dfn-validator) to about `1/sqrt(e) ~= 60.6%`. Indeed, the balance retained by offline [validators](#dfn-validator) after `n` epochs is about `(1-1/INACTIVITY_PENALTY_QUOTIENT)**(n**2/2)` so after `INVERSE_SQRT_E_DROP_TIME` epochs it is roughly `(1-1/INACTIVITY_PENALTY_QUOTIENT)**(INACTIVITY_PENALTY_QUOTIENT/2) ~= 1/sqrt(e)`.
+* The `INACTIVITY_PENALTY_QUOTIENT` equals `INVERSE_SQRT_E_DROP_TIME**2` where `INVERSE_SQRT_E_DROP_TIME := 2**12 epochs` (~18 days) is the time it takes the inactivity penalty to reduce the balance of non-participating [validators](#dfn-validator) to about `1/sqrt(e) ~= 60.6%`. Indeed, the balance retained by offline [validators](#dfn-validator) after `n` epochs is about `(1 - 1/INACTIVITY_PENALTY_QUOTIENT)**(n**2/2)` so after `INVERSE_SQRT_E_DROP_TIME` epochs it is roughly `(1 - 1/INACTIVITY_PENALTY_QUOTIENT)**(INACTIVITY_PENALTY_QUOTIENT/2) ~= 1/sqrt(e)`.
 
 
 ### Max transactions per block
@@ -789,7 +789,7 @@ def decrease_balance(state: BeaconState, index: int, delta: int) -> None:
 ```python
 def get_permuted_index(index: int, list_size: int, seed: Bytes32) -> int:
     """
-    Return `p(index)` in a pseudorandom permutation `p` of `0...list_size-1` with ``seed`` as entropy.
+    Return `p(index)` in a pseudorandom permutation `p` of `0...list_size - 1` with ``seed`` as entropy.
 
     Utilizes 'swap or not' shuffling found in
     https://link.springer.com/content/pdf/10.1007%2F978-3-642-32009-5_1.pdf
@@ -1376,7 +1376,7 @@ def process_deposit(state: BeaconState, deposit: Deposit) -> None:
         # Note: In phase 2 registry indices that have been withdrawn for a long time will be recycled.
         state.validator_registry.append(validator)
         state.balances.append(0)
-        set_balance(state, len(state.validator_registry)-1, amount)
+        set_balance(state, len(state.validator_registry) - 1, amount)
     else:
         # Increase balance by deposit amount
         index = validator_pubkeys.index(pubkey)

From 47477b8e55dba85f7e4e12c3b0cf99bc594ac81d Mon Sep 17 00:00:00 2001
From: Danny Ryan <dannyjryan@gmail.com>
Date: Thu, 21 Mar 2019 09:37:06 -0600
Subject: [PATCH 12/17] cleanup tests to use get_balance and set_balance

---
 .../block_processing/test_process_deposit.py  | 10 ++++----
 tests/phase0/test_sanity.py                   | 23 +++++++++++--------
 2 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/tests/phase0/block_processing/test_process_deposit.py b/tests/phase0/block_processing/test_process_deposit.py
index 297ad37f1..9f1b6add6 100644
--- a/tests/phase0/block_processing/test_process_deposit.py
+++ b/tests/phase0/block_processing/test_process_deposit.py
@@ -5,6 +5,7 @@ import build.phase0.spec as spec
 
 from build.phase0.spec import (
     Deposit,
+    get_balance,
     process_deposit,
 )
 from tests.phase0.helpers import (
@@ -38,8 +39,9 @@ def test_success(state, deposit_data_leaves, pubkeys, privkeys):
     process_deposit(post_state, deposit)
 
     assert len(post_state.validator_registry) == len(state.validator_registry) + 1
-    assert len(post_state.validator_balances) == len(state.validator_balances) + 1
+    assert len(post_state.balances) == len(state.balances) + 1
     assert post_state.validator_registry[index].pubkey == pubkeys[index]
+    assert get_balance(post_state, index) == spec.MAX_DEPOSIT_AMOUNT
     assert post_state.deposit_index == post_state.latest_eth1_data.deposit_count
 
     return pre_state, deposit, post_state
@@ -62,16 +64,16 @@ def test_success_top_up(state, deposit_data_leaves, pubkeys, privkeys):
 
     pre_state.latest_eth1_data.deposit_root = root
     pre_state.latest_eth1_data.deposit_count = len(deposit_data_leaves)
-    pre_balance = pre_state.validator_balances[validator_index]
+    pre_balance = get_balance(pre_state, validator_index)
 
     post_state = deepcopy(pre_state)
 
     process_deposit(post_state, deposit)
 
     assert len(post_state.validator_registry) == len(state.validator_registry)
-    assert len(post_state.validator_balances) == len(state.validator_balances)
+    assert len(post_state.balances) == len(state.balances)
     assert post_state.deposit_index == post_state.latest_eth1_data.deposit_count
-    assert post_state.validator_balances[validator_index] == pre_balance + amount
+    assert get_balance(post_state, validator_index) == pre_balance + amount
 
     return pre_state, deposit, post_state
 
diff --git a/tests/phase0/test_sanity.py b/tests/phase0/test_sanity.py
index 91bd9fe7a..ec03fb355 100644
--- a/tests/phase0/test_sanity.py
+++ b/tests/phase0/test_sanity.py
@@ -21,6 +21,7 @@ from build.phase0.spec import (
     # functions
     get_active_validator_indices,
     get_attestation_participants,
+    get_balance,
     get_block_root,
     get_crosslink_committees_at_slot,
     get_current_epoch,
@@ -28,6 +29,7 @@ from build.phase0.spec import (
     get_state_root,
     advance_slot,
     cache_state,
+    set_balance,
     verify_merkle_branch,
     hash,
 )
@@ -168,7 +170,7 @@ def test_proposer_slashing(state, pubkeys, privkeys):
     assert slashed_validator.exit_epoch < spec.FAR_FUTURE_EPOCH
     assert slashed_validator.withdrawable_epoch < spec.FAR_FUTURE_EPOCH
     # lost whistleblower reward
-    assert test_state.validator_balances[validator_index] < state.validator_balances[validator_index]
+    assert get_balance(test_state, validator_index) < get_balance(state, validator_index)
 
     return state, [block], test_state
 
@@ -203,7 +205,8 @@ def test_deposit_in_block(state, deposit_data_leaves, pubkeys, privkeys):
 
     state_transition(post_state, block)
     assert len(post_state.validator_registry) == len(state.validator_registry) + 1
-    assert len(post_state.validator_balances) == len(state.validator_balances) + 1
+    assert len(post_state.balances) == len(state.balances) + 1
+    assert get_balance(post_state, index) == spec.MAX_DEPOSIT_AMOUNT
     assert post_state.validator_registry[index].pubkey == pubkeys[index]
 
     return pre_state, [block], post_state
@@ -238,12 +241,12 @@ def test_deposit_top_up(state, pubkeys, privkeys, deposit_data_leaves):
     block = build_empty_block_for_next_slot(pre_state)
     block.body.deposits.append(deposit)
 
-    pre_balance = pre_state.validator_balances[validator_index]
+    pre_balance = get_balance(pre_state, validator_index)
     post_state = deepcopy(pre_state)
     state_transition(post_state, block)
     assert len(post_state.validator_registry) == len(pre_state.validator_registry)
-    assert len(post_state.validator_balances) == len(pre_state.validator_balances)
-    assert post_state.validator_balances[validator_index] == pre_balance + amount
+    assert len(post_state.balances) == len(pre_state.balances)
+    assert get_balance(post_state, validator_index) == pre_balance + amount
 
     return pre_state, [block], post_state
 
@@ -412,8 +415,8 @@ def test_transfer(state, pubkeys, privkeys):
     recipient_index = get_active_validator_indices(pre_state.validator_registry, current_epoch)[0]
     transfer_pubkey = pubkeys[-1]
     transfer_privkey = privkeys[-1]
-    amount = pre_state.validator_balances[sender_index]
-    pre_transfer_recipient_balance = pre_state.validator_balances[recipient_index]
+    amount = get_balance(pre_state, sender_index)
+    pre_transfer_recipient_balance = get_balance(pre_state, recipient_index)
     transfer = Transfer(
         sender=sender_index,
         recipient=recipient_index,
@@ -448,8 +451,8 @@ def test_transfer(state, pubkeys, privkeys):
     block.body.transfers.append(transfer)
     state_transition(post_state, block)
 
-    sender_balance = post_state.validator_balances[sender_index]
-    recipient_balance = post_state.validator_balances[recipient_index]
+    sender_balance = get_balance(post_state, sender_index)
+    recipient_balance = get_balance(post_state, recipient_index)
     assert sender_balance == 0
     assert recipient_balance == pre_transfer_recipient_balance + amount
 
@@ -465,7 +468,7 @@ def test_ejection(state):
     assert pre_state.validator_registry[validator_index].exit_epoch == spec.FAR_FUTURE_EPOCH
 
     # set validator balance to below ejection threshold
-    pre_state.validator_balances[validator_index] = spec.EJECTION_BALANCE - 1
+    set_balance(pre_state, validator_index, spec.EJECTION_BALANCE - 1)
 
     post_state = deepcopy(pre_state)
     #

From f6da42ffb32fed8e22769dbf77f906889b1e02a2 Mon Sep 17 00:00:00 2001
From: Danny Ryan <dannyjryan@gmail.com>
Date: Thu, 21 Mar 2019 10:04:20 -0600
Subject: [PATCH 13/17] fix markdown issues

---
 specs/core/0_beacon-chain.md | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 3bc95f717..4eee3dcb5 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -61,9 +61,9 @@
         - [`is_active_validator`](#is_active_validator)
         - [`get_active_validator_indices`](#get_active_validator_indices)
         - [`get_balance`](#get_balance)
-            - [`set_balance`](#set_balance)
-            - [`increase_balance`](#increase_balance)
-            - [`decrease_balance`](#decrease_balance)
+        - [`set_balance`](#set_balance)
+        - [`increase_balance`](#increase_balance)
+        - [`decrease_balance`](#decrease_balance)
         - [`get_permuted_index`](#get_permuted_index)
         - [`get_split_offset`](#get_split_offset)
         - [`get_epoch_committee_count`](#get_epoch_committee_count)
@@ -760,31 +760,32 @@ def get_active_validator_indices(validators: List[Validator], epoch: Epoch) -> L
 def get_balance(state: BeaconState, index: int) -> int:
     return state.balances[index]
 ```
-#### `set_balance`
 
-````python
+### `set_balance`
+
+```python
 def set_balance(state: BeaconState, index: int, balance: int) -> None:
     validator = state.validator_registry[index]
     HALF_INCREMENT = HIGH_BALANCE_INCREMENT // 2
     if validator.high_balance > balance or validator.high_balance + 3 * HALF_INCREMENT < balance:
         validator.high_balance = balance - balance % HIGH_BALANCE_INCREMENT
     state.balances[index] = balance
-````
+```
 
-#### `increase_balance`
+### `increase_balance`
 
-````python
+```python
 def increase_balance(state: BeaconState, index: int, delta: int) -> None:
     set_balance(state, index, get_balance(state, index) + delta)
-````
+```
 
-#### `decrease_balance`
+### `decrease_balance`
 
-````python
+```python
 def decrease_balance(state: BeaconState, index: int, delta: int) -> None:
     cur_balance = get_balance(state, index)
     set_balance(state, index, cur_balance - delta if cur_balance >= delta else 0)
-````
+```
 
 ### `get_permuted_index`
 

From d3f175d7289befde23d9810a29ee1ca40f02216a Mon Sep 17 00:00:00 2001
From: terence tsao <terence@prysmaticlabs.com>
Date: Thu, 21 Mar 2019 11:33:36 -0700
Subject: [PATCH 14/17] Update sync_protocol.md

---
 specs/light_client/sync_protocol.md | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/specs/light_client/sync_protocol.md b/specs/light_client/sync_protocol.md
index 8878545bb..575df60fe 100644
--- a/specs/light_client/sync_protocol.md
+++ b/specs/light_client/sync_protocol.md
@@ -1,6 +1,18 @@
-# Beacon chain light client syncing
+# Beacon Chain Light Client Syncing
+
+__NOTICE__: This document is a work-in-progress for researchers and implementers. One of the design goals of the eth2 beacon chain is light-client friendlines, both to allow low-resource clients (mobile phones, IoT, etc) to maintain access to the blockchain in a reasonably safe way, but also to facilitate the development of "bridges" between the eth2 beacon chain and other chains.
+
+## Table of Contents
+
+<!-- TOC -->
+- [Beacon Chain Light Client Syncing](#beacon-chain-light-client-syncing)
+    - [Table of Contents](#table-of-contents)
+    - [Light client state](#light-client-state)
+    - [Updating the shuffled committee](#updating-the-shuffled-committee)
+    - [Computing the current committee](#computing-the-current-committee)  
+    - [Verifying blocks](#verifying-blocks)      
+<!-- /TOC -->
 
-One of the design goals of the eth2 beacon chain is light-client friendlines, both to allow low-resource clients (mobile phones, IoT, etc) to maintain access to the blockchain in a reasonably safe way, but also to facilitate the development of "bridges" between the eth2 beacon chain and other chains.
 
 ### Preliminaries
 

From 3ece05ccc1a5e126e934c57aa091386a4afeb8ef Mon Sep 17 00:00:00 2001
From: vbuterin <v@buterin.com>
Date: Thu, 21 Mar 2019 16:36:31 -0500
Subject: [PATCH 15/17] Small cosmetic change to slashable attestations

---
 specs/core/0_beacon-chain.md | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 1067c3dc0..c7c74279f 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -182,7 +182,7 @@ Code snippets appearing in `this style` are to be interpreted as Python code.
 | `SHARD_COUNT` | `2**10` (= 1,024) |
 | `TARGET_COMMITTEE_SIZE` | `2**7` (= 128) |
 | `MAX_BALANCE_CHURN_QUOTIENT` | `2**5` (= 32) |
-| `MAX_INDICES_PER_SLASHABLE_VOTE` | `2**12` (= 4,096) |
+| `MAX_SLASHABLE_ATTESTATION_PARTICIPANTS` | `2**12` (= 4,096) |
 | `MAX_EXIT_DEQUEUES_PER_EPOCH` | `2**2` (= 4) |
 | `SHUFFLE_ROUND_COUNT` | 90 |
 
@@ -1159,7 +1159,7 @@ def verify_slashable_attestation(state: BeaconState, slashable_attestation: Slas
     if slashable_attestation.custody_bitfield != b'\x00' * len(slashable_attestation.custody_bitfield):  # [TO BE REMOVED IN PHASE 1]
         return False
 
-    if len(slashable_attestation.validator_indices) == 0:
+    if not (1 <= len(slashable_attestation.validator_indices) <= MAX_SLASHABLE_ATTESTATION_PARTICIPANTS):
         return False
 
     for i in range(len(slashable_attestation.validator_indices) - 1):
@@ -1169,9 +1169,6 @@ def verify_slashable_attestation(state: BeaconState, slashable_attestation: Slas
     if not verify_bitfield(slashable_attestation.custody_bitfield, len(slashable_attestation.validator_indices)):
         return False
 
-    if len(slashable_attestation.validator_indices) > MAX_INDICES_PER_SLASHABLE_VOTE:
-        return False
-
     custody_bit_0_indices = []
     custody_bit_1_indices = []
     for i, validator_index in enumerate(slashable_attestation.validator_indices):

From e313c5ba5abd949e2af87919a36f84937ee6b68c Mon Sep 17 00:00:00 2001
From: Danny Ryan <dannyjryan@gmail.com>
Date: Thu, 21 Mar 2019 17:08:54 -0600
Subject: [PATCH 16/17] add tests for proposer slashing

---
 .../test_process_proposer_slashing.py         | 97 +++++++++++++++++++
 tests/phase0/helpers.py                       | 44 +++++++++
 tests/phase0/test_sanity.py                   | 39 +-------
 3 files changed, 144 insertions(+), 36 deletions(-)
 create mode 100644 tests/phase0/block_processing/test_process_proposer_slashing.py

diff --git a/tests/phase0/block_processing/test_process_proposer_slashing.py b/tests/phase0/block_processing/test_process_proposer_slashing.py
new file mode 100644
index 000000000..467d2164b
--- /dev/null
+++ b/tests/phase0/block_processing/test_process_proposer_slashing.py
@@ -0,0 +1,97 @@
+from copy import deepcopy
+import pytest
+
+import build.phase0.spec as spec
+from build.phase0.spec import (
+    get_balance,
+    get_current_epoch,
+    process_proposer_slashing,
+)
+from tests.phase0.helpers import (
+    get_valid_proposer_slashing,
+)
+
+# mark entire file as 'header'
+pytestmark = pytest.mark.proposer_slashings
+
+
+def run_proposer_slashing_processing(state, proposer_slashing, valid=True):
+    """
+    Run ``process_proposer_slashing`` returning the pre and post state.
+    If ``valid == False``, run expecting ``AssertionError``
+    """
+    post_state = deepcopy(state)
+
+    if not valid:
+        with pytest.raises(AssertionError):
+            process_proposer_slashing(post_state, proposer_slashing)
+        return state, None
+
+    process_proposer_slashing(post_state, proposer_slashing)
+
+    slashed_validator = post_state.validator_registry[proposer_slashing.proposer_index]
+    assert not slashed_validator.initiated_exit
+    assert slashed_validator.slashed
+    assert slashed_validator.exit_epoch < spec.FAR_FUTURE_EPOCH
+    assert slashed_validator.withdrawable_epoch < spec.FAR_FUTURE_EPOCH
+    # lost whistleblower reward
+    assert (
+        get_balance(post_state, proposer_slashing.proposer_index) <
+        get_balance(state, proposer_slashing.proposer_index)
+    )
+
+    return state, post_state
+
+
+def test_success(state):
+    proposer_slashing = get_valid_proposer_slashing(state)
+
+    pre_state, post_state = run_proposer_slashing_processing(state, proposer_slashing)
+
+    return pre_state, proposer_slashing, post_state
+
+
+def test_epochs_are_different(state):
+    proposer_slashing = get_valid_proposer_slashing(state)
+
+    # set slots to be in different epochs
+    proposer_slashing.header_2.slot += spec.SLOTS_PER_EPOCH
+
+    pre_state, post_state = run_proposer_slashing_processing(state, proposer_slashing, False)
+
+    return pre_state, proposer_slashing, post_state
+
+
+def test_headers_are_same(state):
+    proposer_slashing = get_valid_proposer_slashing(state)
+
+    # set headers to be the same
+    proposer_slashing.header_2 = proposer_slashing.header_1
+
+    pre_state, post_state = run_proposer_slashing_processing(state, proposer_slashing, False)
+
+    return pre_state, proposer_slashing, post_state
+
+
+def test_proposer_is_slashed(state):
+    proposer_slashing = get_valid_proposer_slashing(state)
+
+    # set proposer to slashed
+    state.validator_registry[proposer_slashing.proposer_index].slashed = True
+
+    pre_state, post_state = run_proposer_slashing_processing(state, proposer_slashing, False)
+
+    return pre_state, proposer_slashing, post_state
+
+
+def test_proposer_is_withdrawn(state):
+    proposer_slashing = get_valid_proposer_slashing(state)
+
+    # set proposer withdrawable_epoch in past
+    current_epoch = get_current_epoch(state)
+    proposer_index = proposer_slashing.proposer_index
+    state.validator_registry[proposer_index].withdrawable_epoch = current_epoch - 1
+
+    pre_state, post_state = run_proposer_slashing_processing(state, proposer_slashing, False)
+
+    return pre_state, proposer_slashing, post_state
diff --git a/tests/phase0/helpers.py b/tests/phase0/helpers.py
index 5c61685a6..3987289bf 100644
--- a/tests/phase0/helpers.py
+++ b/tests/phase0/helpers.py
@@ -7,14 +7,18 @@ from build.phase0.utils.minimal_ssz import signed_root
 from build.phase0.spec import (
     # constants
     EMPTY_SIGNATURE,
+    ZERO_HASH,
     # SSZ
     AttestationData,
+    BeaconBlockHeader,
     Deposit,
     DepositInput,
     DepositData,
     Eth1Data,
+    ProposerSlashing,
     VoluntaryExit,
     # functions
+    get_active_validator_indices,
     get_block_root,
     get_current_epoch,
     get_domain,
@@ -199,3 +203,43 @@ def build_deposit(state,
     )
 
     return deposit, root, deposit_data_leaves
+
+
+def get_valid_proposer_slashing(state):
+    current_epoch = get_current_epoch(state)
+    validator_index = get_active_validator_indices(state.validator_registry, current_epoch)[-1]
+    privkey = pubkey_to_privkey[state.validator_registry[validator_index].pubkey]
+    slot = state.slot
+
+    header_1 = BeaconBlockHeader(
+        slot=slot,
+        previous_block_root=ZERO_HASH,
+        state_root=ZERO_HASH,
+        block_body_root=ZERO_HASH,
+        signature=EMPTY_SIGNATURE,
+    )
+    header_2 = deepcopy(header_1)
+    header_2.previous_block_root = b'\x02' * 32
+    header_2.slot = slot + 1
+
+    domain = get_domain(
+        fork=state.fork,
+        epoch=get_current_epoch(state),
+        domain_type=spec.DOMAIN_BEACON_BLOCK,
+    )
+    header_1.signature = bls.sign(
+        message_hash=signed_root(header_1),
+        privkey=privkey,
+        domain=domain,
+    )
+    header_2.signature = bls.sign(
+        message_hash=signed_root(header_2),
+        privkey=privkey,
+        domain=domain,
+    )
+
+    return ProposerSlashing(
+        proposer_index=validator_index,
+        header_1=header_1,
+        header_2=header_2,
+    )
diff --git a/tests/phase0/test_sanity.py b/tests/phase0/test_sanity.py
index ec03fb355..444075a13 100644
--- a/tests/phase0/test_sanity.py
+++ b/tests/phase0/test_sanity.py
@@ -46,6 +46,7 @@ from tests.phase0.helpers import (
     build_deposit_data,
     build_empty_block_for_next_slot,
     force_registry_change_at_next_epoch,
+    get_valid_proposer_slashing,
 )
 
 
@@ -117,42 +118,8 @@ def test_empty_epoch_transition_not_finalizing(state):
 
 def test_proposer_slashing(state, pubkeys, privkeys):
     test_state = deepcopy(state)
-    current_epoch = get_current_epoch(test_state)
-    validator_index = get_active_validator_indices(test_state.validator_registry, current_epoch)[-1]
-    privkey = privkeys[validator_index]
-    slot = spec.GENESIS_SLOT
-    header_1 = BeaconBlockHeader(
-        slot=slot,
-        previous_block_root=ZERO_HASH,
-        state_root=ZERO_HASH,
-        block_body_root=ZERO_HASH,
-        signature=EMPTY_SIGNATURE,
-    )
-    header_2 = deepcopy(header_1)
-    header_2.previous_block_root = b'\x02' * 32
-    header_2.slot = slot + 1
-
-    domain = get_domain(
-        fork=test_state.fork,
-        epoch=get_current_epoch(test_state),
-        domain_type=spec.DOMAIN_BEACON_BLOCK,
-    )
-    header_1.signature = bls.sign(
-        message_hash=signed_root(header_1),
-        privkey=privkey,
-        domain=domain,
-    )
-    header_2.signature = bls.sign(
-        message_hash=signed_root(header_2),
-        privkey=privkey,
-        domain=domain,
-    )
-
-    proposer_slashing = ProposerSlashing(
-        proposer_index=validator_index,
-        header_1=header_1,
-        header_2=header_2,
-    )
+    proposer_slashing = get_valid_proposer_slashing(state)
+    validator_index = proposer_slashing.proposer_index
 
     #
     # Add to state via block transition

From 11c3291817f3d590723298877c41d0bf244b789b Mon Sep 17 00:00:00 2001
From: terence tsao <terence@prysmaticlabs.com>
Date: Thu, 21 Mar 2019 16:30:45 -0700
Subject: [PATCH 17/17] Update sync_protocol.md

---
 specs/light_client/sync_protocol.md | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/specs/light_client/sync_protocol.md b/specs/light_client/sync_protocol.md
index 8878545bb..143f82a39 100644
--- a/specs/light_client/sync_protocol.md
+++ b/specs/light_client/sync_protocol.md
@@ -40,8 +40,8 @@ def get_later_start_epoch(slot: Slot) -> int:
     return slot - slot % PERSISTENT_COMMITTEE_PERIOD - PERSISTENT_COMMITTEE_PERIOD
     
 def get_earlier_period_data(block: ExtendedBeaconBlock, shard_id: Shard) -> PeriodData:
-    period_start = get_earlier_start_epoch(header.slot)
-    validator_count = len(get_active_validator_indices(state, period_start))
+    period_start = get_earlier_start_epoch(block.slot)
+    validator_count = len(get_active_validator_indices(block.state, period_start))
     committee_count = validator_count // (SHARD_COUNT * TARGET_COMMITTEE_SIZE) + 1
     indices = get_shuffled_committee(block.state, shard_id, period_start, 0, committee_count)
     return PeriodData(
@@ -51,8 +51,8 @@ def get_earlier_period_data(block: ExtendedBeaconBlock, shard_id: Shard) -> Peri
     )
     
 def get_later_period_data(block: ExtendedBeaconBlock, shard_id: Shard) -> PeriodData:
-    period_start = get_later_start_epoch(header.slot)
-    validator_count = len(get_active_validator_indices(state, period_start))
+    period_start = get_later_start_epoch(block.slot)
+    validator_count = len(get_active_validator_indices(block.state, period_start))
     committee_count = validator_count // (SHARD_COUNT * TARGET_COMMITTEE_SIZE) + 1
     indices = get_shuffled_committee(block.state, shard_id, period_start, 0, committee_count)
     return PeriodData(