Goal:
  
  A : Type
  B : Type
  p : A → B → bool
  a : A
  l : list A
  b : B
  l' : list B
  q : list A
  q' : list B
  IHl : ∀ l' : list B,
          forallb2 p l l' && forallb2 p q q' → forallb2 p (l ++ q) (l' ++ q')
  pa : is_true (p a b)
  pl : is_true (forallb2 p l l')
  pq : is_true (forallb2 p q q')
  ============================
   (is_true (p a b && forallb2 p (l ++ q) (l' ++ q')))


DEBUG:Going to execute:
rewrite pa IHl // pl pq
DEBUG LTAC Evaluated term: andb_and
DEBUG LTAC Evaluated term: (iffLR
                              (Q:=p a b && forallb2 p l l' ∧ forallb2 p q q')
                              (andb_and (p a b && forallb2 p l l')
                                 (forallb2 p q q')) _view_subject_)
DEBUG LTAC Evaluated term: andb_and
DEBUG LTAC Evaluated term: (iffLR (Q:=p a b ∧ forallb2 p l l')
                              (andb_and (p a b) (forallb2 p l l'))
                              _view_subject_)