Thank you for the clear answer. The only thing I wish that there was more information about mathcolumn (/MC) command on the wiki.

with \startmathcases ... \stopmathcases you get a curly bracket to the left of "...", see [1]. If you just want to have multiline equations, then \startalign ... \stopalign could be want you need (it's also on page [1]). There's also a "My Way" [2] about mathalign.

-- Best Regards, Vyatcheslav Yatskovsky