mathlib

8cd16b97 - feat(category_theory/sums): sums (disjoint unions) of categories (#1357)

feat(category_theory/sums): sums (disjoint unions) of categories (#1357) * feat(category_theory/sum): direct sums of categories * minor * tidying * Fix white space, remove old comments * rearranging, associator * add TODO comment about unitors * fix import * create /basic.lean files