# Space group for cubic structure

Hello all,

I am having trouble figuring out the space group for a cubic structure having A atoms at 000 and B atoms at 1/2 1/2 0, 1/2 0 1/2 & 0 1/2 1/2. Now, I know that it is Pm3m, but what is confusing me is why is there not a 4 fold axis at the first m, thus, giving you a P(4/m)3m? And when you have a tetragonal structure with A atoms at 000 & 1/2 1/2 0 and B atoms at 1/2 0 1/2 & 0 1/2 1/2 you get a P(4/m)mm!?! Please give any help you can. And if you know of any websites of several examples with answers, please let me know. Thanks for any help!