Little maths question

[Mark Smith]

This is probably really easy, but I'm so stupid when it comes to maths 
that I can't figure it out:

Given a list of any number of lines, how can I generate a list of every 
possible combination of those lines ie.

1
2
3
4

would give:

1
2
3
4
1,2
1,3
1,4
2,3
2,4
3,4
1,2,3
1,3,4
2,3,4
1,2,3,4
(this is from my thick head, so may not be complete, but you get the 
idea...)

Thanks,

Mark