Goal:
    A : Type  B : Type  C : Type  R : A → B → C → Type  H : True
  ============================
   (let H := CoreTactics.block in
    let H0 := CoreTactics.block in All3_nil = All3_nil)


DEBUG:Going to execute:
let eliminator := eval simpl in DepElim.elim in
           tac p eliminator
DEBUG LTAC Evaluated term: H
DEBUG LTAC Evaluated term: True