Goal:
  
  A : Type
  P : A → A → Type
  hd : A
  tl : list A
  tl' : list A
  a : OnOne2 P tl tl'
  hd0 : A
  tl0 : list A
  tl'0 : list A
  b : OnOne2 P tl0 tl'0
  ============================
   (∀ (H := CoreTactics.block) (e : NoConfusion_OnOne2 A P
                                      {|
                                        pr1 :=
                                          {|
                                            pr1 := hd :: tl; pr2 := hd :: tl'
                                          |};
                                        pr2 := OnOne2_tl P hd tl tl' a
                                      |}
                                      {|
                                        pr1 :=
                                          {|
                                            pr1 := hd0 :: tl0;
                                            pr2 := hd0 :: tl'0
                                          |};
                                        pr2 := OnOne2_tl P hd0 tl0 tl'0 b
                                      |}),
      let H0 := CoreTactics.block in
      noConfusion_OnOne2_obligation_2 A P
        {|
          pr1 := {| pr1 := hd :: tl; pr2 := hd :: tl' |};
          pr2 := OnOne2_tl P hd tl tl' a
        |}
        {|
          pr1 := {| pr1 := hd0 :: tl0; pr2 := hd0 :: tl'0 |};
          pr2 := OnOne2_tl P hd0 tl0 tl'0 b
        |}
        (noConfusion_OnOne2_obligation_1 A P
           {|
             pr1 := {| pr1 := hd :: tl; pr2 := hd :: tl' |};
             pr2 := OnOne2_tl P hd tl tl' a
           |}
           {|
             pr1 := {| pr1 := hd0 :: tl0; pr2 := hd0 :: tl'0 |};
             pr2 := OnOne2_tl P hd0 tl0 tl'0 b
           |} e) = e)


DEBUG:Going to execute:
match T with
           | context [ CoreTactics.block ] =>
               change T; CoreTactics.intros_until_block
           end