# Placing equation number on left with reqno option in amsart document class

Is there a way to force individual equations to place their equation numbers (or more specifically the result of a \tag*{blah}) on a specific side of the page regardless of the options to amsart.

I sometimes wish to use the equation enviornment to define 'requirements' in my papers which should look like:

R_e: equation stuff

Where R_e is the equation tag. R_e should be on the left even when reqno is passed to the documentclass. How can I accomplish this?

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If you just want to do this for the equation environment, define a command to be used in the equation environment:

\newcommand{\LeftEqNo}{\let\veqno\@@leqno}


For instance,

\documentclass{article}
\usepackage{amsmath}
\makeatletter
\newcommand{\LeftEqNo}{\let\veqno\@@leqno}
\makeatother
\begin{document}
$$x^2 + y^2 = 1,$$
$$\LeftEqNo x^2 + y^2 = 1.$$
\end{document}


The align environment is implemented quite differently, and you will need the environ package used like

\usepackage{environ}
\makeatletter
\NewEnviron{Lalign}{\tagsleft@true\begin{align}\BODY\end{align}}
\makeatother


Then use \begin{Lalign} ... \end{Lalign} for left-numbered align environments.

I'm afraid that various hacks of the same kind will be necessary for the other ams environments, but I can't list everything without knowing which ones you need :).

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equation or possibly align is fine. I plan to wrap this in a special environment for this construct and it will be one of those two. – Peter Gerdes Jan 2 '11 at 0:18
When I try this (using pdflatex) I get an error: ! Undefined control sequence. \env@Lalign@process ->\tagsleft – Sam Nead Sep 9 '11 at 14:59
@Sam Nead: I assume you might have a different version of the environ package. Can you post somewhere the result of \listfiles? – Bruno Le Floch Sep 11 '11 at 17:17
Using the command \LeftEqNo in equation as above, LaTeX reports the error "ERROR: You can't use \spacefactor' in display math mode." and "\veqno ->\spacefactor \@m l.1567 ". What is wrong? – gofvonx Feb 6 '14 at 10:16
@gofvonx I've updated with a full example. I had forgotten to mention the need for \makeatletter and \makeother when one works with commands whose name contains @`. – Bruno Le Floch Feb 7 '14 at 22:32