mathlib3

6c97ce02 - feat(category_theory): some natural isomorphisms related to composition by functors (#2189)

feat(category_theory): some natural isomorphisms related to composition by functors (#2189) * feat(category_theory): some natural isomorphisms related to composition by functors * tidy up * cleanup * fix * better design Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>