Goal:
  
  A : Type
  B : Type
  C : Type
  D : Type
  R : C → D → Type
  f : A → C
  g : B → D
  b : B
  l' : list B
  ============================
   ({| pr1 := []; pr2 := g b :: map g l' |} = {| pr1 := []; pr2 := [] |}
    → 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:
simplify * || simplify ?; cbv beta