def groups_per_user(group_dictionary):
	"""The groups_per_user function receives a dictionary, which contains group names
	with the list of users. Users can belong to multiple groups. It returns a
	dictionary with the users as keys and a list of their groups as values."""
	user_groups = {}
	for group, users in group_dictionary.items():
		for user in users:
			if user not in user_groups:
				user_groups[user] = []
			user_groups[user].append(group)
	return(user_groups)