Goal:
  
  A : Type
  B : Type
  P : B → A → A → Type
  b0 : B
  bs : list B
  hd : A
  tl : list A
  tl' : list A
  a : OnOne2All P bs tl tl'
  b : B
  bs0 : list B
  hd0 : A
  hd' : A
  tl0 : list A
  p : P b hd0 hd'
  e : #|bs0| = #|tl0|
  ============================
   (∀ (H := CoreTactics.block) (e0 : NoConfusion_OnOne2All A B P
                                       {|
                                         pr1 :=
                                           {|
                                             pr1 := b0 :: bs;
                                             pr2 :=
                                               {|
                                                 pr1 := hd :: tl;
                                                 pr2 := hd :: tl'
                                               |}
                                           |};
                                         pr2 :=
                                           OnOne2All_tl P b0 bs hd tl tl' a
                                       |}
                                       {|
                                         pr1 :=
                                           {|
                                             pr1 := b :: bs0;
                                             pr2 :=
                                               {|
                                                 pr1 := hd0 :: tl0;
                                                 pr2 := hd' :: tl0
                                               |}
                                           |};
                                         pr2 :=
                                           OnOne2All_hd P b bs0 hd0 hd' tl0 p
                                             e
                                       |}),
      let H0 := CoreTactics.block in
      noConfusion_OnOne2All_obligation_2 A B P
        {|
          pr1 :=
            {|
              pr1 := b0 :: bs; pr2 := {| pr1 := hd :: tl; pr2 := hd :: tl' |}
            |};
          pr2 := OnOne2All_tl P b0 bs hd tl tl' a
        |}
        {|
          pr1 :=
            {|
              pr1 := b :: bs0;
              pr2 := {| pr1 := hd0 :: tl0; pr2 := hd' :: tl0 |}
            |};
          pr2 := OnOne2All_hd P b bs0 hd0 hd' tl0 p e
        |}
        (noConfusion_OnOne2All_obligation_1 A B P
           {|
             pr1 :=
               {|
                 pr1 := b0 :: bs;
                 pr2 := {| pr1 := hd :: tl; pr2 := hd :: tl' |}
               |};
             pr2 := OnOne2All_tl P b0 bs hd tl tl' a
           |}
           {|
             pr1 :=
               {|
                 pr1 := b :: bs0;
                 pr2 := {| pr1 := hd0 :: tl0; pr2 := hd' :: tl0 |}
               |};
             pr2 := OnOne2All_hd P b bs0 hd0 hd' tl0 p e
           |} e0) = e0)


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