feat(combinatorics/simple_graph): add three useful lemmas relating walk.support and walk.append (#15687)
feat(combinatorics/simple_graph): add three useful lemmas relating walk.support and walk.append (#15687)

Co-authored-by: Kyle Miller <04892e540c93233cb5dfa2674fa5218f82feced5@gmail.com>



Co-authored-by: Kyle Miller <04892e540c93233cb5dfa2674fa5218f82feced5@gmail.com>

leanprover-community/mathlib,leanprover-community/mathlib