simp only [Set.subset_def]
Node : Type
inst✝ : DecidableEq Node
g : Graph Node
xs ys : List Node
h1 : xs ⊆ ys
⊢ reachable_from_list g xs ⊆ reachable_from_list g ys
Node : Type
inst✝ : DecidableEq Node
g : Graph Node
xs ys : List Node
h1 : xs ⊆ ys
⊢ ∀ x ∈ reachable_from_list g xs, x ∈ reachable_from_list g ys