use x, b, L₁, L₂
case not
α : Type
inst✝ : DecidableEq α
L L' L₁ L₂ : List (α × Bool)
x : α
b : Bool
⊢ ∃ x_1 b_1 L₁_1 L₂_1,
    L₁ ++ (x, b) :: (x, !b) :: L₂ = L₁_1 ++ (x_1, b_1) :: (x_1, !b_1) :: L₂_1 ∧ L₁ ++ L₂ = L₁_1 ++ L₂_1
no goals