Goal:
  
  A : Type
  P : list A → A → Type
  l : list A
  a : All_fold P l
  b : All_fold P l
  H : NoConfusionHom_All_fold A P l a b
  ============================
   (a = b)


DEBUG:Going to execute:
CoreTactics.destruct_sigma a; CoreTactics.destruct_sigma b;
            destruct a; DepElim.depelim b; simpl in * |-;
            CoreTactics.on_last_hyp
             ltac:(fun id =>
                     hnf in id;
                      CoreTactics.destruct_tele_eq id || DepElim.depelim id)