Goal:
  
  A : Type
  B : Type
  C : Type
  R : A → B → C → Type
  l0 : list A
  l1 : list B
  l : list C
  a : All3 R l0 l1 l
  ============================
   (noConfusionHom_All3_obligation_1 A B C R l0 l1 l a a
      (noConfusionHom_All3_obligation_2 A B C R l0 l1 l a a eq_refl) =
    eq_refl)


DEBUG:Going to execute:
fun id =>
             match type of id with
             | sigma ?P =>
                 let idx := fresh "idx" in
                 destruct id as [idx id];
                  repeat CoreTactics.destruct_sigma idx; 
                  simpl in id
             | _ => idtac
             end