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
  b : All3 R l0 l1 l
  e : NoConfusionHom_All3 A B C R l0 l1 l a b
  ============================
   (noConfusionHom_All3_obligation_2 A B C R l0 l1 l a b
      (noConfusionHom_All3_obligation_1 A B C R l0 l1 l a b e) = e)


DEBUG:Going to execute:
CoreTactics.destruct_sigma a; CoreTactics.destruct_sigma b;
            destruct a; DepElim.depelim b; simpl in * |-