simp
case right
α : Type u_1
l✝ : List α
pairs✝ : List (α × α)
h✝ : pairs✝ = build_pairs l✝
l : List α
pairs : List (α × α)
p : α × α
x : α
xs : List α
h : pairs = build_pairs.pairs x xs ++ build_pairs xs
in_pairs : p ∈ build_pairs.pairs x xs ∨ p ∈ build_pairs xs
in_build_pairs : p ∈ build_pairs xs
⊢ p.snd ∈ x :: xs
case right
α : Type u_1
l✝ : List α
pairs✝ : List (α × α)
h✝ : pairs✝ = build_pairs l✝
l : List α
pairs : List (α × α)
p : α × α
x : α
xs : List α
h : pairs = build_pairs.pairs x xs ++ build_pairs xs
in_pairs : p ∈ build_pairs.pairs x xs ∨ p ∈ build_pairs xs
in_build_pairs : p ∈ build_pairs xs
⊢ p.snd = x ∨ p.snd ∈ xs