I am trying to have multiple alignment in my equation in addition to line breaking. Here is a MWE illustrating my problem:
\documentclass[10pt]{article}
\usepackage[T1]{fontenc}
\usepackage{amsmath, amsthm, amssymb}
\usepackage[ansinew]{inputenc}
\begin{alignat*}{2}
a\quad &: \quad \alpha &= +1 + 2 \\
\phantom{a\quad : \quad}-3 + 4 \notag\\
a\quad &: \quad \beta &= +4
\end{alignat*}
\end{document}
The middle equation is not aligned correctly, the minus sign should of course appear right below/above the other two plus-signs.