[R] Plotmath issue superscript "-"

[Gavin Simpson]

Dear List,

I'm trying to typeset some chemical ions in axis labels. These have both
super and subscript components, and for some, I need a superscript "-".
In LaTeX I might use $NO_3^-$ to do the typesetting, but I'm having a
problem getting the correct invocation for expression:

> expression(NO^{-}[3])
Error: syntax error, unexpected '}' in "expression(NO^{-}"
> expression(NO^-[3])
Error: syntax error, unexpected '[' in "expression(NO^-["
> expression(NO^-)
Error: syntax error, unexpected ')' in "expression(NO^-)"
> expression(NO^{-})
Error: syntax error, unexpected '}' in "expression(NO^{-}"

This is with R 2.5.1 (exact version info below).

I suspect this is something to do with my use of the "-", which has some
special meaning.

Is there a way to achieve a superscript "-" (or similar looking
character) using the plotmath routines in R?

Thanks in advance,

G

> version
               _                                          
platform       i686-pc-linux-gnu                          
arch           i686                                       
os             linux-gnu                                  
system         i686, linux-gnu                            
status         Patched                                    
major          2                                          
minor          5.1                                        
year           2007                                       
month          07                                         
day            05                                         
svn rev        42131                                      
language       R                                          
version.string R version 2.5.1 Patched (2007-07-05 r42131)

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