[Xy-pic] Thicker arrows

[Michael Abbott]

> How can I increase the thickness of arrows?

The answer is kinda clunky, but the following works well enough for me:

1.  Put the following definition in your preamble:

	\newcommand{\myar}{\ar@[|(3)]}

2.  Use \myar instead of \ar in all your xymatrix diagrams.

You'll need to use dvips output, as this command uses a postscript command
to enlarge the arrows, but it seems to work well enough.

Your question about making the xymatrix fill the page width is odd: an
xymatrix diagram has an intrinsic size, so there is no option to stretch
the diagram.  Your best bet is to play with line and column spacing.