Is it possible to have amsmath automatically number equations in "subequations" style, when a multiline construct like
\begin{align}
E &= m c^2 \\
c^2 &= a^2 + c^2
\end{align}
is encountered?
Using the subequations environment explicitly is useful, when it is necessary to refer to a group of equations. When the only reason for using it is a style requirement, that successive equations should be numbered as (13a), (13b), etc., it would however be nice to have this automated away.
Additionally, this would be extremely useful in LyX, where using the Subequations module breaks the layout of the live-preview.