TeX source:

\left\{\mathrm{f}\left(\mathrm{a}_{1}\right), \mathrm{f}\left(\mathrm{a}_{2}\right), \mathrm{f}\left(\mathrm{a}_{3}\right), \mathrm{f}\left(\mathrm{a}_{4}\right), \ldots\right\}=\{2,2,2, \ldots\}