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


DEBUG:Going to execute:
simplify * || simplify ?; cbv beta