Data structure correctness

Ensure data structures are accurately represented with their proper constraints and valid implementations, particularly for recursive structures. When documenting or implementing collections:

1. Explicitly state data structure constraints
   • For set-like structures, clearly document hashability requirements
   • For tree-like structures, describe node relationships precisely
2. Validate that recursive type examples actually terminate
   • Include escape conditions in recursive type definitions
   • Ensure examples represent structures that can be instantiated

# Incorrect recursive type definition (infinite recursion)
type B = list[C]
type C = B  # No termination condition!

# Correct recursive type definition with termination
type A = list[A] | None  # Terminates with None

Properly defined data structures not only prevent runtime errors but also enable more efficient algorithm implementations.