[R] greek letters do not work in expression

[Milan Cisty]

Dear all,
I appreciate suggestions for following problem. I wrote to RStudio:
plot(c(1,20),c(1,20), xlab = expression(paste(alfa)))
or the same happen when I wrote:
plot(c(1,20),c(1,20), xlab = expression(alfa))
what happen is, that description under x label is exactly "alpha", not greek
letter alfa (α).
Please where should I search problem, or what information to sent to list for
identification of this problem?
Thanks,
Milan