mathlib

0f5ea396 - feat(order/antichain, order/minimal): some antichain lemmas (#14507)

feat(order/antichain, order/minimal): some antichain lemmas (#14507) This PR adds a few lemmas about antichains, including their images under complementation and order isomorphisms. Co-authored-by: Floris van Doorn <fpvdoorn@gmail.com>