Plot two graphs in a same plot

I would like to plot y1 and y2 in the same plot.

x  <- seq(-2, 2, 0.05)y1 <- pnorm(x)y2 <- pnorm(x, 1, 1)plot(x, y1, type = "l", col = "red")plot(x, y2, type = "l", col = "green")

But when I do it like this, they are not plotted in the same plot together.

In Matlab one can do hold on, but does anyone know how to do this in R?