Goal:
    A : Type  B : Type  R : nat → A → B → Type  n : nat  H : True
  ============================
   (let H := CoreTactics.block in
    let H0 := CoreTactics.block in All2i_nil = All2i_nil)


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