Goal:
  
  A : Type
  P : list A → A → Type
  b0 : All_fold P []
  b' : list A
  b : All_fold P b'
  ============================
   ({| pr1 := []; pr2 := b0 |} = {| pr1 := b'; pr2 := b |}
    → ∀ (H := CoreTactics.block) (e : NoConfusionHom_All_fold A P []
                                        (All_fold_nil P) b0),
        let H0 := CoreTactics.block in
        noConfusionHom_All_fold_obligation_2 A P [] 
          (All_fold_nil P) b0
          (noConfusionHom_All_fold_obligation_1 A P [] (All_fold_nil P) b0 e) =
        e)


DEBUG:Going to execute:
hnf in id
Level 5: evaluation returns
hnf in id;
 match type of id with
 | sigma _ =>
     let xn := fresh id "'" in
     destruct id as [xn id]; DepElim.decompose_exists xn id;
      cbv beta iota delta [TODO projection TODO projection] in id, id';
      DepElim.decompose_exists id id'
 | _ => cbv beta iota delta [TODO projection TODO projection] in id, id'
 end
where
id' := b
of type
constr
id := b
of type
constr of type tacvalue