I have just learned about cosets and meet with the following question.
Find all left cosets of the subgroup generated by $\overline a$ in $\mathbb Z_{12}$. I know $\mathbb Z_{12} = \{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11\}$. I would like to know (for example if $a=2$). What does $\overline a$ mean here? Thanks.