r - Greek and alpha numeric in ggplot2 axis labels -

i use ggplot2 make chart axis label of ul, 'u' greek 'mu'.
add mu, have found work

p <- ggplot(data.frame(x = 1:3, y = 1:3), aes(x= x, y=y)) + geom_point() p + ylab(expression(mu)) 

but have not been able place else alongside it. these not work

p + ylab(paste(expression(mu), "foo")) p + ylab("expression(mu)~foo") 

thanks in advance

sam

how this:

p <- ggplot(data.frame(x = 1:3, y = 1:3), aes(x= x, y=y)) + geom_point() p + ylab(expression(paste(mu,l)))