[R] scalable < > delimiters in plotmath

[baptiste auguie]

Dear list,

I read in ?plotmath that I can use bgroup to draw scalable delimiters
such as [ ] and ( ). The same technique fails with < > however, and I
cannot find a workaround,

grid.text(expression(bgroup("<",atop(x,y),">")))

Error in bgroup("<", atop(x, y), ">") : invalid group delimiter

Regards,

baptiste

sessionInfo()
R version 2.11.1 (2010-05-31)
x86_64-apple-darwin9.8.0

locale:
[1] en_GB.UTF-8/en_GB.UTF-8/C/C/en_GB.UTF-8/en_GB.UTF-8

attached base packages:
[1] grid      stats     graphics  grDevices utils     datasets
methods   base

other attached packages:
[1] TeachingDemos_2.7

loaded via a namespace (and not attached):
[1] tools_2.11.1