mathlib3

87cf6e36 - feat(category_theory/category_of_elements) (#990)

feat(category_theory/category_of_elements) (#990) * feat(category_theory/category_of_elements) * Update src/category_theory/elements.lean Co-Authored-By: semorrison <scott@tqft.net> * Update src/category_theory/elements.lean Co-Authored-By: semorrison <scott@tqft.net> * Update src/category_theory/elements.lean Co-Authored-By: semorrison <scott@tqft.net> * Update src/category_theory/punit.lean Co-Authored-By: semorrison <scott@tqft.net> * various * remaining simp lemmas