∀ (motive : (cs : List Char) → (cs = [] ∨ ∃ l' b, cs = l'.concat b) → Prop) (cs : List Char)
  (x : cs = [] ∨ ∃ l' b, cs = l'.concat b),
  (∀ (a : Unit), motive [] ⋯) → (∀ (cs : List Char) (c : Char), motive (cs.concat c) ⋯) → motive cs x