Aligning long broken equation (with brackets also split over multiple lines)

Question

I have long equation $F=\left\{ abcdef \right\}$ which needed to break line at halfway. To do it I use \begin{multline}.

\begin{multline}
 F =  \left\{   abc \right.\nonumber\\
 \left. {}  +  def \right\},
\end{multline}

I also need to break curly bracket over the multiple lines, which I do with \right.\nonumber\\.

q1) How to align the equals sign of top line with + sign of bottom line in this case?

q2) How to display equation number?

Answer 1

First option does what you want, although I prefer second solution with + not aligned with =.

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{mathtools}
\begin{document}

\begin{equation}
\begin{split}
F = & \left\{ abc \right.\\
   + & \left. def \right\}
\end{split}
\end{equation}

\begin{equation}
\begin{split}
F = & \left\{ abc \right.\\
    & + \left. def \right\}
\end{split}
\end{equation}
\end{document}