# A and B irreducible representations?

In character tables, I know that A and B are one-dimensional irreducible representations, but what is the difference them?

And why do some character tables list them as A1/A2, B1/B2 and others have Au/Ag, Bu/Bg?

• g|u are from the German terms for even|odd, 1|2 are for people who doesn't care to remember those, and the difference is all there in the tables. Also, welcome to Chem.SE. – Ivan Neretin Aug 5 '16 at 7:02

You can see, for example, that $C_n$ groups of even order have both A and B representations, while those of odd order cannot feature B representations.