mathlib3

7a52b9ce - feat(category_theory/groupoid/subgroupoid): subgroupoids and basic properties (#16742)

feat(category_theory/groupoid/subgroupoid): subgroupoids and basic properties (#16742) Add a definition of (bundled) subgroupoid and prove some of their basic properties. Co-authored-by: Rémi Bottinelli <remi.bottinelli@bluewin.ch> Co-authored-by: bottine <bottine@users.noreply.github.com>