mathlib

6379d39e - feat(data/set/countable): protect lemmas (#15415)

feat(data/set/countable): protect lemmas (#15415) We protect `set.countable_iff_exists_injective`, `set.countable_iff_exists_surjective`, and `set.countable.to_encodable` in order to avoid clashes with the theorems on the new `countable` typeclass.