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 : False
  ============================
   ({|
      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
    |})


DEBUG:Going to execute:
fun H =>
             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