Goal:
  
  A : Type
  B : Type
  C : Type
  D : Type
  R : C → D → Type
  f : A → C
  g : B → D
  b : B
  l' : list B
  H1' : list C
  H1 : list D
  ============================
   (All2 R H1' H1
    → {| pr1 := []; pr2 := g b :: map g l' |} = {| pr1 := H1'; pr2 := H1 |}
      → let H := CoreTactics.block in
        let H0 := CoreTactics.block in
        All2 (λ (x : A) (y : B), R (f x) (g y)) [] (b :: l'))


DEBUG:Going to execute:
intros p