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
  tl0 : list A
  tl'0 : list A
  b1 : OnOne2All P bs0 tl0 tl'0
  ============================
   (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 := hd0 :: tl'0 |}
          |};
        pr2 := OnOne2All_tl P b bs0 hd0 tl0 tl'0 b1
      |}
    → let H := CoreTactics.block in
      {|
        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 := hd0 :: tl'0 |}
          |};
        pr2 := OnOne2All_tl P b bs0 hd0 tl0 tl'0 b1
      |})


DEBUG:Going to execute:
CoreTactics.intros_until_block
DEBUG LTAC Evaluated term: (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 := hd0 :: tl'0
                                      |}
                                  |};
                                pr2 := OnOne2All_tl P b bs0 hd0 tl0 tl'0 b1
                              |}
                            → let H := CoreTactics.block in
                              {|
                                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 := hd0 :: tl'0
                                      |}
                                  |};
                                pr2 := OnOne2All_tl P b bs0 hd0 tl0 tl'0 b1
                              |})