intro a a1
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 : Node), x_1 ∈ xs ∨ x_1 ∈ S → x_1 = x ∨ (x_1 ∈ xs ∨ x_1 ∈ zs) ∨ x_1 ∈ ys
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
a : Node
a1 : a ∈ xs ∨ a ∈ S
⊢ a = x ∨ (a ∈ xs ∨ a ∈ zs) ∨ a ∈ ys