Goal:
  
  A : Type
  B : Type
  P : A → nat → B → Type
  n : nat
  X : Alli (λ (n : nat) (y : B), All (λ x : A, P x n y) []) n []
  ============================
   (All (λ x : A, Alli (P x) n []) [])


DEBUG:Going to execute:
constructor => //=