ggplot2 subscript in x-axis labels(ticks, legend)

#==============================
# ggplot2: subscript in x-axis labels(ticks)
rm(list=ls(all=TRUE))
library(ggplot2)
data <- data.frame(names=tolower(LETTERS[1:4]),mean_p=runif(4))

p <- ggplot(data,aes(x=names,y=mean_p))
p <- p + geom_bar(colour="black",fill="white")
p <- p + xlab("expressions") + scale_y_continuous(expression(paste("Wacky Data")))
p <- p + scale_x_discrete(labels=c(a=expression(paste(Delta^2)),
                               b=expression(paste(q^n)),
                               c=expression(log(z)),
                               d=expression(paste(omega / (x + 13)^2))))

p

# from: http://stackoverflow.com/questions/6202667/how-to-use-subscripts-in-ggplot2-legends-r

#==============================
# ggplot2: subscript in y-axis labels
rm(list=ls(all=TRUE))
library(ggplot2)
dat <- data.frame(x = rnorm(100), y = rnorm(100))
ggplot(dat, aes(x=x,y=y)) +
     geom_point() +
     labs(y=expression(Blah[1*d]))

ggplot(dat, aes(x=x,y=y)) +
     geom_point() +
     labs(y=expression(Blah["1d"]))
    
ggplot(dat, aes(x=x,y=y)) +
    geom_point() +
    labs(y=expression(Blah[1*d]*"%"))    
    
# from: http://stackoverflow.com/questions/17334759/subscript-letters-in-ggplot-axis-label
# http://stackoverflow.com/questions/8514478/subscripts-in-xlabels-in-ggplot2
# http://stackoverflow.com/questions/15125628/putting-mathematical-symbols-and-subscripts-mixed-with-regular-letters-in-r-ggpl
# http://www.janeshdevkota.com/blog/using-superscripts-and-subscripts-in-ggplot2/