simp only [Set.subset_def]
Node : Type
inst✝ : DecidableEq Node
g : Graph Node
x : Node
⊢ reachable_from_list g (direct_succ_list g x) ⊆ reachable_from_list g [x]
Node : Type
inst✝ : DecidableEq Node
g : Graph Node
x : Node
⊢ ∀ x_1 ∈ reachable_from_list g (direct_succ_list g x), x_1 ∈ reachable_from_list g [x]