p.dnorm (mu = 0, s = 1, h0.col = "light gray",
         ms.lines = TRUE, ms.col = "gray", ...)
p.dchisq(nu,    h0.col = "light gray", ...)
p.dgamma(shape, h0.col = "light gray", ...)

p.dnorm()
p.dnorm(mu=1.5, add = TRUE, ms.lines = FALSE) # add to the plot above

p.dchisq(2, main= "Chi^2 Densities -- nu = 2,3,4")
p.dchisq(3, add = TRUE, col = "red")
p.dchisq(4, add = TRUE, col = "blue")

op <- par(mfrow = c(2,2), mgp = c(1.6, 0.6,0), mar = c(3,3,1,1))
for(sh in 1:4)
   p.dgamma(sh)
par(op)