mathlib

81311088 - feat(category_theory/opposites): add nat_iso.unop (#2132)

feat(category_theory/opposites): add nat_iso.unop (#2132) * Add nat_iso.unop * Add docstrings to nat_iso.op, nat_iso.unop Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>