Alright here’s a puzzler for you all. This code: (define xs (set 1 2 3)) (define/contract checked-xs (set/c number? #:lazy? lazy?) xs) (set-add checked-xs 'foo) …runs without error if lazy? is false, but throws an error at the set-add expression if lazy? is true. Now, I get why this happens: the lazily-checked variant of set/c decided that insertions into the (immutable, persistent) set should satisfy the contract as well. My question for you all is: is this inconsistency bad? If racket/set were to be redesigned, would you change it? And what if lazy contracts were the default, would your answers to these questions change?