Goal:
  
  A : Type
  B : Type
  p : A → B → bool
  l : list A
  l' : list B
  q : list A
  q' : list B
  ============================
   (forallb2 p l l' && forallb2 p q q' → forallb2 p (l ++ q) (l' ++ q'))


DEBUG:Going to execute:
induction l in l' |- *; destruct l'; simpl