Goal:
  
  A : Type
  P : nat → A → Type
  k : nat
  l : list A
  alli : Alli (λ k' : nat, P (Nat.pred #|List.rev l| - k' + k)) 0 l
  ============================
   (Alli (λ k' : nat, P (Nat.pred #|l| - k' + k)) 0 l)


DEBUG:Going to execute:
autorewrite with len in cl