simp only [← mem_direct_succ_list_iff]
Node : Type
inst✝ : DecidableEq Node
g : Graph Node
x : Node
xs : List Node
⊢ {y | ∃ x_1 ∈ x :: xs, ∃ ys, y ∈ ys ∧ (x_1, ys) ∈ g} =
    ↑(direct_succ_list g x).toFinset ∪ {y | ∃ x ∈ xs, ∃ ys, y ∈ ys ∧ (x, ys) ∈ g}
Node : Type
inst✝ : DecidableEq Node
g : Graph Node
x : Node
xs : List Node
⊢ {y | ∃ x_1 ∈ x :: xs, y ∈ direct_succ_list g x_1} =
    ↑(direct_succ_list g x).toFinset ∪ {y | ∃ x ∈ xs, y ∈ direct_succ_list g x}