def equivalence_partition( iterable, relation ):
	"""Partitions a set of objects into equivalence classes
	
	Args:
		iterable: collection of objects to be partitioned
		relation: equivalence relation. I.e. relation(o1,o2) evaluates to True
			if and only if o1 and o2 are equivalent
			
	Returns: classes, partitions
		classes: A sequence of sets. Each one is an equivalence class
		partitions: A dictionary mapping objects to equivalence classes
	"""
	classes = []
	partitions = { }
	for o in iterable: # for each object
		# find the class it is in
		found = False
		for c in classes:
			if relation( iter(c).next(), o ): # is it equivalent to this class?
				c.add( o )
				partitions[o] = c
				found = True
				break
		if not found: # it is in a new class
			classes.append( set( [ o ] ) )
			partitions[o] = classes[-1]
	return classes, partitions