Back with more questions on confusing discrete maths stuff. Sets are much easier than the logic stuff though. And we've started predicate logic which is just brain melting :S

Anyway. If all these are true what can be said about A and B:
A union B = A
A intersect B = A
A\B = A
A\B = B\A

Given the last one I'm thinking A and B are both empty sets.

There's probably a crap joke involving four Swedes there, but my brain is too akin to mushy peas at present to squeeze anything out.

:D Took me too long to get that. This stuff turns my brain to mushy peas.

If you want mush, look at the code for any average software and somewhere you'll find nested inverted double negative conditional crap that'll tie you in knots requiring a miniature octopus to undo.

For A union B and A intersect B to be the same value, then every element in A must also be in B - i.e. A contains nothing that B doesn't contain, and B contains nothing that A doesn't contain.

I don't know what A\B is, but if it's symmetric difference then it appears to mean matching values in B are removed from A to get the result - so A\B=A means that no elements in B are in A, and since A doesn't contain anything B doesn't, then they are both empty.

The last one is saying A without B is the same as B without A - that means both sets contain the same elements (i.e. same as first two lines), but doesn't on it's own say that they are the empty set - the third line is needed to confirm that.

Probably.

Yes that's all correct.

Although I did A union B means B is a subset or equal to A. Then A setminus/difference B must mean B is empty. Then A intersect B, or A intersect empty set means A is also empty set.

Not sure the last line is required.

The answer to this one was:
a) B is a subset of A
b) A is a subset of B
c) A and B are disjoint sets
d) The two sets are identical

so I only got 1 out of 4 for that. Pff.