simp only [Set.subset_def]
Node : Type
inst : DecidableEq Node
xs ys zs : List Node
S : Set Node
x : Node
h1 : ∀ x_1 ∈ S, (x_1 = x ∨ x_1 ∈ zs) ∨ x_1 ∈ ys
⊢ ↑xs.toFinset ∪ S ⊆ ↑xs.toFinset ∪ ↑zs.toFinset ∪ ({x} ∪ ↑ys.toFinset)
Node : Type
inst : DecidableEq Node
xs ys zs : List Node
S : Set Node
x : Node
h1 : ∀ x_1 ∈ S, (x_1 = x ∨ x_1 ∈ zs) ∨ x_1 ∈ ys
⊢ ∀ x_1 ∈ ↑xs.toFinset ∪ S, x_1 ∈ ↑xs.toFinset ∪ ↑zs.toFinset ∪ ({x} ∪ ↑ys.toFinset)