Value vs. Reference Semantics, see:
- ImmutableValue
- ValueObject
- ValueObjectHypotheses
- ValueObjectsCanBeMutable
- ValueObjectsShouldBeImmutable
- ValueObjectsShouldBePassedByValue
- ValueSemantics
Also, what should ( #( 1 2 3) asSet = #( 1 3 2) asSet ) answer? Looks like assignment to me ;)