Goal:
  
  A : Type
  P : list A → A → Type
  l : list A
  a : All_fold P l
  b : All_fold P l
  e : NoConfusionHom_All_fold A P l a b
  ============================
   (noConfusionHom_All_fold_obligation_2 A P l a b
      (noConfusionHom_All_fold_obligation_1 A P l a b e) = e)


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