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|
  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 H := 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 goal with
           | |- let _ := CoreTactics.block in _ => intros _
           | |- _ => try (intro; CoreTactics.intros_until_block)
           end