simp [cancP, nonnil_nextVertex_cancel, nilP]
α : Type
inst✝ : DecidableEq α
start : List (α × Bool)
letter : α × Bool
nilP : ¬start = []
cancP : List.getLast start nilP = letter⁻¹
⊢ List.concat start letter ∼ start :+ letter
α : Type
inst✝ : DecidableEq α
start : List (α × Bool)
letter : α × Bool
nilP : ¬start = []
cancP : List.getLast start nilP = letter⁻¹
⊢ start ++ [letter] ∼ List.dropLast start