Goal:
  
  X : Type
  Y : Type
  R : nat → X → Y → Type
  n : nat
  x : X
  y : Y
  l : list X
  r : list Y
  r0 : R n x y
  a : All2i R (S n) l r
  IHa : #|l| = #|r|
  ============================
   (S #|l| = S #|r|)


DEBUG:Going to execute:
intros; Zify.zify_pre_hook; zify_elim_let; zify_op;
            Zify.zify_iter_specs; Zify.zify_to_euclidean_division_equations;
            Zify.zify_post_hook