def is_prefix(s1, s2):
	"""
	Checks if s1 and s2 have the same prefix. Two itemsets have the same prefix if they are the same
	except for the last item. Both itemsets should be sorted following the alphabetical order
	:param s1: First itemset
	:param s2: Second itemset
	:return: True if s1 and s2 have the same prefix
	"""
	return s1[:-1] == s2[:-1]