Goal:
  
  A : Type
  B : Type
  R : A → B → Type
  R' : ∀ (a : A) (b : B), R a b → Type
  x : A
  y : B
  l : list A
  l' : list B
  r : R x y
  rs : All2 R l l'
  r0 : R' x y r
  a0 : All2_dep R' rs
  b : All2_dep R' (All2_cons r rs)
  b0 := {|
          pr1 :=
            {|
              pr1 := x :: l;
              pr2 := {| pr1 := y :: l'; pr2 := All2_cons r rs |}
            |};
          pr2 := b
        |}
     : sigma
         (λ index : sigma
                      (λ xs : list A, sigma (λ ys : list B, All2 R xs ys)),
            All2_dep R' (pr2 (pr2 index)))
  ============================
   (let H := CoreTactics.block in
    NoConfusionHom_All2_dep A B R R' (x :: l) (y :: l') 
      (All2_cons r rs) (All2_dep_cons r0 a0) b
    → let H0 := CoreTactics.block in All2_dep_cons r0 a0 = b)


DEBUG:Going to execute:
hnf in (type of id')