simp [cancP, nilP, nonnil_nextVertex_cancel] at eq1
α : Type
inst✝ : DecidableEq α
start : List (α × Bool)
letter : α × Bool
reduced_start : Reduced start
nilP : ¬start = []
L' : List (α × Bool)
step : Step (start :+ letter) L'
x : α
b : Bool
L₁ L₂ : List (α × Bool)
eqs : start :+ letter = L₁ ++ (x, b) :: (x, !b) :: L₂ ∧ L' = L₁ ++ L₂
eq1 : start :+ letter = L₁ ++ (x, b) :: (x, !b) :: L₂ := eqs.left
cancP : List.getLast start nilP = letter⁻¹
⊢ False
α : Type
inst✝ : DecidableEq α
start : List (α × Bool)
letter : α × Bool
reduced_start : Reduced start
nilP : ¬start = []
L' : List (α × Bool)
step : Step (start :+ letter) L'
x : α
b : Bool
L₁ L₂ : List (α × Bool)
eqs : start :+ letter = L₁ ++ (x, b) :: (x, !b) :: L₂ ∧ L' = L₁ ++ L₂
cancP : List.getLast start nilP = letter⁻¹
eq1 : List.dropLast start = L₁ ++ (x, b) :: (x, !b) :: L₂
⊢ False