list of unique non-subset sets

[les_ander at yahoo.com]

Hi,
I have many set objects some of which can contain same group of object
while others can be subset of the other. Given a list of sets,
I need to get a list of unique sets such that non of the set is an
subset of another or contain exactly the same members.

Tried to do the following:
s1=set(['a','b','c'])
s2=set(['a','c'])
s3=set(['a','d','e','f'])
s4=set(['r','k','l'])
s5=set(['r','k','l'])
L=[s1,s2,s3,s4,s5]
----------------------- > cleaned-up list should contain s1, s3, s5

Lu=[] # unique list of sets
Lu.append( L[0] )
for i in range(1,len(L)):
 s=L[i]
 # check for equality
 if s in L:
    continue
 # check for subseting
 for j in len(Lu):
    s1=Lu[j]
    if len (s-s1)==0:
          continue
    elif len(s1-s)==0:
        Lu[i]=s1 # replace with the bigger


But this does not work since I get
Lu=[set(['a', 'c', 'b'])]

What am I doing wrong?
thanks