##\mathbb{Z}_p## (also denoted as the quotient group ##\mathbb{Z}/p\mathbb{Z})## is the set of residue classes modulo ##p##. So for example, ##\mathbb{Z}_5=\{0,1,2,3,4\}##. In the above example, ##\rtimes## denotes the semi direct product, as opposed to ##\times## which is the direct product...