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From: ogawa@orion.arc.nasa.gov (Arthur Ogawa)
Newsgroups: comp.text.tex
Subject: Re: Two-column layouts in LaTeX
Summary: LaTeX: No switching between single and double column within a page
Keywords: LaTeX switching columns
Message-ID: <1991Jan25.174137.9997@news.arc.nasa.gov>
Date: 25 Jan 91 17:41:37 GMT
References: <15987@sdcc6.ucsd.edu>
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LaTeX definitely provides no way to switch between single and double column
mode within a page (balancing the columns as it goes). Ideally, the \onecolumn
and \twocolumn macros should provide this functionality.

In working up the macro package for the Mathematica Journal, I added such 
functionality to LaTeX's output routine, so I know it is possible.
I think I saw an article in TugBoat by Frank Mittelbach in which he does this,
too (but without providing for floats).