Goal:
    A : Type  B : Type  C : Type  R : A → B → C → Type  H : True
  ============================
   (All3_nil = All3_nil)


DEBUG:Going to execute:
(DepElim.is_introduced H; CoreTactics.block_goal;
             CoreTactics.revert_until H; CoreTactics.block_goal) ||
             (let H' := fresh H in
              intros until H'; CoreTactics.block_goal) ||
               (intros; CoreTactics.block_goal)