diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index c3ae4102e..6e7433758 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -532,7 +532,7 @@ def get_active_shard_count(state: BeaconState) -> uint64:
 ```python
 def get_online_validator_indices(state: BeaconState) -> Set[ValidatorIndex]:
     active_validators = get_active_validator_indices(state, get_current_epoch(state))
-    return set([i for i in active_validators if state.online_countdown[i] != 0])
+    return set(i for i in active_validators if state.online_countdown[i] != 0)  # non-duplicate
 ```
 
 #### `get_shard_committee`
diff --git a/specs/phase1/custody-game.md b/specs/phase1/custody-game.md
index e454e28c0..8bcfc0433 100644
--- a/specs/phase1/custody-game.md
+++ b/specs/phase1/custody-game.md
@@ -554,7 +554,6 @@ def process_custody_slashing(state: BeaconState, signed_custody_slashing: Signed
         slash_validator(state, custody_slashing.whistleblower_index)
 ```
 
-
 ## Per-epoch processing
 
 ### Handling of reveal deadlines
@@ -586,7 +585,7 @@ def process_custody_final_updates(state: BeaconState) -> None:
 
     # Reset withdrawable epochs if challenge records are empty
     records = state.custody_chunk_challenge_records
-    validator_indices_in_records = set([record.responder_index for record in records])
+    validator_indices_in_records = set(record.responder_index for record in records)  # non-duplicate
     for index, validator in enumerate(state.validators):
         if validator.exit_epoch != FAR_FUTURE_EPOCH:
             not_all_secrets_are_revealed = validator.all_custody_secrets_revealed_epoch == FAR_FUTURE_EPOCH
diff --git a/specs/phase1/validator.md b/specs/phase1/validator.md
index 130765268..954193d25 100644
--- a/specs/phase1/validator.md
+++ b/specs/phase1/validator.md
@@ -162,7 +162,7 @@ def get_shard_winning_roots(state: BeaconState,
         committee = get_beacon_committee(state, on_time_attestation_slot, committee_index)
 
         # Loop over all shard transition roots, looking for a winning root
-        shard_transition_roots = set([a.data.shard_transition_root for a in shard_attestations])
+        shard_transition_roots = set(a.data.shard_transition_root for a in shard_attestations)  # non-duplicate
         for shard_transition_root in sorted(shard_transition_roots):
             transition_attestations = [
                 a for a in shard_attestations