I would like to vertically smash a summation sign in a way that the line has a vertical space as if the summation sign wouldn't be there.
To illustrate it please see the MWE. The space between the first and second line should be the same as the space between the third and fourth line. At the moment it looks like the second line doesn't belong to the first one.
Note: I cannot write the last column into one line, because the second column will contain more text in the end and I have to break the last column into two or multiple lines.
MWE:
\documentclass{scrbook}
\usepackage{amsmath}
\begin{document}
\begin{alignat}{3}
& \sum_{m \in M} x_m && = 1 & \quad & , \forall m \in M \colon a \neq b ; \notag \\
& && & & \phantom{,{}} c \neq d \\
& x_m && = 1 & & , \forall m \in M \colon e \neq f ; \notag \\
& && & & \phantom{,{}} g \neq h
\end{alignat}
\end{document}