Goal:
  
  A : Type
  B : Type
  C : Type
  P : nat → A → B → Type
  Q : B → C → Type
  R : B → C → Type
  l'' : list C
  n : nat
  H1' : list B
  H1 : list C
  H : All2 Q H1' H1
  ============================
   ({| pr1 := []; pr2 := l'' |} = {| pr1 := H1'; pr2 := H1 |}
    → let H := CoreTactics.block in
      let H0 := CoreTactics.block in
      (∀ (n : nat) (x : A) (y : B) (z : C), P n x y → Q y z → R y z)
      → All2 R [] l'')


DEBUG:Going to execute:
fun tac p =>
             let ty := type of p in
             let eliminator := eval simpl in DepElim.elim in
             tac p eliminator