Goal:
  
  A : Type
  B : Type
  C : Type
  R : A → B → C → Type
  b : All3 R [] [] []
  H : NoConfusionHom_All3 A B C R [] [] [] All3_nil b
  ============================
   (All3_nil = b)


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)