fact: Definition hexagon_join_assoc_sym A B C : functor_join (join_sym A B) idmap o join_assoc A B C o trijoin_id_sym A C B == join_assoc B A C o join_sym (Join A C) B o join_assoc A C B.
imports: Basics Types WildCat Join.Core Join.TriJoin Spaces.Nat.Core