How to make an equation system with right brackets on “two levels”

Question

does someone know how to make these "double" right brackets? I have not been able to find a solution.

Best, Tiziano

Answer 1

With reference to A lateral brace to group a set of equations with labels, here is an option:

\documentclass{article}

\usepackage{amsmath,empheq,amssymb,zref-savepos}

\begin{document}

\begin{empheq}[right={\empheqrbrace\ \forall t \in \mathbb{N}}]{align}
                  f(x) &= ax^2 + bx + c\zsaveposy{top}
  \raisebox{-.5\dimexpr\zposy{top}sp-\zposy{bot}sp}[0pt][0pt]{$
    \hspace{15pt}\left.\rule{0pt}{\dimexpr\zposy{top}sp-\zposy{bot}sp}\right\}\ \forall i \in \mathbb{N}
  $} \\
         ax^2 + bx + c &= g(x)\zsaveposy{bot} \\
                  h(x) &= dx^3 + ex^2 + fx + h \hspace{35pt} \\
  dx^3 + ex^2 + fx + h &= i(x)
\end{empheq}

\end{document}

Answer 2

tikz can be useful for this task, because the braces are nested such that using empheq won't be easy. Using an overlay picture, the braces don't interfere with how the equations are laid out.

\documentclass{article}
\usepackage{amsmath,tikz}
\begin{document}

\newcommand{\tkzmark}[1]{\tikz[remember picture, overlay]{\coordinate(#1);}}

\begin{align}
eq1\tkzmark{0} \\
eq2\tkzmark{1}  \\
eq3 \\
eq4
\end{align}

\begin{tikzpicture}[remember picture, overlay]
\node at ([shift={(.5em,-.5em)}]0)[right] {$\left.\rule{0pt}{1.2\baselineskip}\right\} \forall i \in N$};
\node at ([shift={(5em,-.5em)}]1)[right] {$\left.\rule{0pt}{2.5\baselineskip}\right\} \forall t \in N$};
\end{tikzpicture}

\end{document}