Goal:
  
  A : Type
  B : Type
  A' : Type
  B' : Type
  R : A' → B' → Prop
  f : A → A'
  g : B → B'
  h : Forall2 R (map f []) (map g [])
  ============================
   (Forall2 (λ (x : A) (y : B), R (f x) (g y)) [] [])


DEBUG:Going to execute:
<coq-core.plugins.ltac::constructor@0>
Level 0: Backtrace:

Proof is not complete.
Level 0: Backtrace:

No applicable tactic.