Here's a possibility, but clearly not optimal:
Code: Select all
\newcommand\rightalign[1]{\noalign{\vbox{\hfill $\displaystyle #1$}}}
\begin{align*}
A&=B1
\\
&=B2a
\\
\rightalign{B2b}
&=B3
\end{align*}
Code: Select all
\newcommand\rightalign[1]{\noalign{\vbox{\hfill $\displaystyle #1$}}}
\begin{align*}
A&=B1
\\
&=B2a
\\
\rightalign{B2b}
&=B3
\end{align*}
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