English
Every edge in a walk is an edge of the graph, proved by induction on the walk.
Русский
Каждое ребро обхода принадлежит ребрам графа; доказательство по индукции по обходу.
LaTeX
$$$\forall p:\\ G.Walk u v,\\ e:\\ Sym2 V,\\ e \in p.\\edges \Rightarrow e \in G.edgeSet$$$
Lean4
/-- Every edge in a walk's edge list is an edge of the graph.
It is written in this form (rather than using `⊆`) to avoid unsightly coercions. -/
theorem edges_subset_edgeSet {u v : V} : ∀ (p : G.Walk u v) ⦃e : Sym2 V⦄, e ∈ p.edges → e ∈ G.edgeSet
| cons h' p', e, h => by
cases h
· exact h'
next h' => exact edges_subset_edgeSet p' h'