mathlib

d329d6bd - feat(combinatorics/simple_graph/connectivity): walks, paths, cycles (#10981)

feat(combinatorics/simple_graph/connectivity): walks, paths, cycles (#10981) This is the first chunk of #8737, which gives a type for walks in a simple graph as well as some basic operations. It is designed to one day generalize to other types of graphs once there is a more generic framework by swapping out the `G.adj u v` argument from `walk`.