symbolic pdf's and cdf'sin the "distrib" package



After loading the "distrib" package, is it possible to 
somehow obtain the symbolic form of, say, pdf_gamma(x,a,b)? 
  Typing "pdf_gamma(x,a,b)" returns simply "pdf_gamma(x,a,b)".
After looking at the distrib code, I tried "assume(x>0)" 
first, but that didn't make any difference.

					Kostas