[R] Double inequality with plotmath

[Mark Seeto]

Hello,

I'm fairly new to R and I can't work out how to produce a double
inequality like (LaTeX) $0 \leq x \leq 1$ in the legend of a graph. If
I try

> legend(50, 0.1, legend = c(expression(0 <= x <= 1), c(2 <= x <= 3)), pch = c(1,1), col = c(2, 3))

then I get an error message "unexpected '<=' in ...". I've checked the
help files for plotmath and expression, but could not find a solution.

I would appreciate any help you can give.

Thanks,
Mark