Goal:
  
  A : Type
  P : A → A → Type
  hd : A
  hd' : A
  tl : list A
  p : P hd hd'
  hd0 : A
  tl0 : list A
  tl' : list A
  b : OnOne2 P tl0 tl'
  e : False
  ============================
   (noConfusion_OnOne2_obligation_2 A P
      {|
        pr1 := {| pr1 := hd :: tl; pr2 := hd' :: tl |};
        pr2 := OnOne2_hd P hd hd' tl p
      |}
      {|
        pr1 := {| pr1 := hd0 :: tl0; pr2 := hd0 :: tl' |};
        pr2 := OnOne2_tl P hd0 tl0 tl' b
      |}
      (noConfusion_OnOne2_obligation_1 A P
         {|
           pr1 := {| pr1 := hd :: tl; pr2 := hd' :: tl |};
           pr2 := OnOne2_hd P hd hd' tl p
         |}
         {|
           pr1 := {| pr1 := hd0 :: tl0; pr2 := hd0 :: tl' |};
           pr2 := OnOne2_tl P hd0 tl0 tl' b
         |} e) = e)


DEBUG:Going to execute:
match type of H with
           | ?R ?x ?y =>
               let rhs := fresh in
               set (rhs := y) in *; pattern sigma rhs; clearbody rhs;
                destruct H; simpl
           end