Multi-plot

  Create a new graphics window between plots.
  You don't say what operating system you're using: for Unix, x11() is the
command to create a new window; for Windows, I believe it's windows() (see
?Devices).
  Then see ?dev.cur() for information on how you can list, switch between
graphics windows, etc.

  Q to gurus: is there a simple way to get the command for the default
graphics driver, something like options()$createdevice [options$device is
useful but "X11" can't quite be turned into x11() without some hacking,
and I don't know if that hack would work generally].  You can always write
a little bit of conditional code, but I'm just wondering if there's a
simple one-liner ...