def sequence(seq, limits=None):
 seq = sympify(seq)
 if is_sequence(seq, Tuple):
  return SeqPer(seq, limits)
 else:
  return SeqFormula(seq, limits)

def sequence ( seq , limits = None ) : seq = sympify ( seq ) if is_sequence ( seq , Tuple ) : return SeqPer ( seq , limits ) else : return SeqFormula ( seq , limits )
yields an infinite sequence .