Goal:
  
  A : Type
  B : Type
  C : Type
  R : A → C → Type
  g : A → B → C
  y : B
  ys : list B
  ============================
   (0 = S #|ys|
    → All2 R [] [] → All2 (λ (x : A) (y : B), R x (g x y)) [] (y :: ys))


DEBUG:Going to execute:
hnf