Goal:
  
  A : Type
  P : list A → A → Type
  d : A
  Γ : list A
  a : All_fold P Γ
  p : P Γ d
  b0 : All_fold P (d :: Γ)
  b : sigma (λ index : list A, All_fold P index)
  ============================
   ({| pr1 := d :: Γ; pr2 := b0 |} = b
    → ∀ (H := CoreTactics.block) (e : NoConfusionHom_All_fold A P 
                                        (d :: Γ) (All_fold_cons P a p) b0),
        let H0 := CoreTactics.block in
        noConfusionHom_All_fold_obligation_2 A P (d :: Γ)
          (All_fold_cons P a p) b0
          (noConfusionHom_All_fold_obligation_1 A P 
             (d :: Γ) (All_fold_cons P a p) b0 e) = e)


DEBUG:Going to execute:
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