Goal:
  
  A : Type
  B : Type
  k : nat
  Q : nat → A → Type
  R : nat → A → B → Type
  l : list A
  l' : list B
  n : nat
  q1' : nat
  q1 : list A
  q : Alli Q q1' q1
  ============================
   ({| pr1 := n; pr2 := [] |} = {| pr1 := q1'; pr2 := q1 |}
    → let H := CoreTactics.block in
      let H0 := CoreTactics.block in
      All2i (λ (i : nat) (x : A) (y : B), Q i x × R i x y) n [] [])


DEBUG:Going to execute:
DepElim.decompose_exists id id'