First of all, I'm not sure these environments are supposed to be nested, but the fact is the alignment comes out exactly how I wanted, and no errors are issued.
\documentclass[a5paper]{article}
\usepackage{amsmath}
\begin{document}
\begin{gather}
\begin{align}
a &= b + c \notag \\
%\label{important}
b - a &= -c \\
c - a &= -b
\end{align} \\
a - (b-a) - (c-a) = 2a
\end{gather}
\end{document}
The problem appears when I uncomment the \label
, then compilation is interrupted with:
! Package amsmath Error: Multiple \label's: label 'important' will be lost.
The result is still OK, and I wouldn't mind too much if I didn't have to press enter every time I compile...
I could bypass amsmath
's redefinition of \label
as shown here, but is there another possible fix? Or am I doing something fundamentally wrong?