\input{_preamble}
\begin{document}
    \myeqs{
        \boldsymbol{U}^{(k)}
        =\left\{u_i^{(k)}\right\}
        \equiv\overunderbraces{
            &&\br{5}{\text{domain}\vphantom{p}}
        }{
            \left\{\vphantom{u^{(k)}}\right.
            &u_{0}^{(k)},\dots,&u_{p-k}^{(k)}&,
            &u_{p-k+1}^{(k)}, \dots,u_{n-k}^{(k)}
            &,&u_{n+1-k}^{(k)}&,\dots,u_{n+p+1-2k}^{(k)}& \left.\vphantom{u^{(k)}}\right\}}
        {&\br{2}{p-k+1}&&\br{1}{n-p}&&\br{2}{1+p-k}},\quad
        u_{i}^{(k)}\leq u_{i+1}^{(k)},
    }
\end{document}