can't plot ylab in graph

Dear People,

I am sure I am missing something obvious as usual, but in the following
graph I can't plot ylab.

Ignoring unimportant details, I am plotting one instance of truehist() and
one instance of curve() on the same graph. Truehist() won't let me pass
the ylab argument. It gives me the error

Error in plot.default(xlim, c(0, ymax), type = "n", xlab = xlab, ylab =
"",  : formal argument "ylab" matched by multiple actual arguments

I don't understand the error. I looked at the help page for truehist().
The xlab argument was present but the ylab argument was missing.

I can pass the argument to curve but it is ignored. I tried adding it to
the line par(new=T) below, but that didn't do anything either.

Thanks in advance for any help.

                                                   Faheem.

************************************************************************

mg.hist <- function(len,theta,pos,size)
{
  x <- empmargdistvec(len,theta,pos,size)

  postscript(file="plot.ps", horizontal = FALSE, onefile = FALSE, paper
             = "special", width=6, height=4)
  par(mfcol=c(1,2),pch=20)

  truehist(x, nbins=100,xlab=expression(paste("Range ", (theta))))

  mydensityfn <- function(x)
    {
      mydensity(x,theta,pos,len)
    }
  par(new=T)
  curve(mydensityfn, col = "red", add=TRUE)

...
}