∀ {V : Type u_1} {G : SimpleGraph V} [inst : Fintype V] (H : G.Subgraph) (a b : V),
  (H.verts.toFinset, fun a b => decide (H.Adj a b)).2 a b = true →
    a ∈ (H.verts.toFinset, fun a b => decide (H.Adj a b)).1