nelson beebe has asked about a problem that arose when he tried this with

                   {\hrule \begin{equation}}

sorry, nelson -- that's a feature, not a bug.

here's what it says in the file technote.tex that's distributed with the
ams-latex collection.

\section{Why can't I use abbreviations for the \env{equation}

Many users have discovered to their dismay that when switching from
ordinary \latex/ to the \pkg{amsmath} package, they are no longer able
to use abbreviations such as |\beq| |\eeq| for |\begin{equation}|
|\end{equation}|. This has to do with unfortunately nontrivial technical
complications: the environments such as \env{align} must read their
contents as a delimited macro argument because they do multipass
processing of the contents using algorithms inherited from Spivak's
\fn{amstex.tex}. The obvious solution---substitution of different
algorithms that do box shuffling instead of token shuffling for the
multipass calculations---would require rewriting these display
environments from the ground up; while that is a worthy goal, it was
beyond the original scope of the \amslatex/ project. Some progress has
in fact been made on such a solution [time of writing: January 1995],
but not yet to the point of being ready for release.

Users have proposed two workarounds (September 1996):
\item |\def\beq#1\eeq{\begin{equation}#1\end{equation}}| (Donald Arseneau)
\item Define |\newcommand{\env}[2]{\begin{#1}#2\end{#1}}| and then use
  |\env{equation}{...}| (Michael Skeide)


this may change in the future, but i'm not going to hold *my* breath.
                                                -- bb