function () 
{
    x = seq(0, 30, 0.1)
    dfs = c(2, 5, 10, 20)
    ychisq = dchisq(x, 1)
    i = 1
    plot(x, ychisq, type = "l", xlab = "s", ylab = "density", 
        ylim = c(0, 0.5), col = i)
    for (df in dfs) {
        i = i + 1
        lines(x, dchisq(x, df), col = i, lty = i)
    }
    legend(10, 0.5, c("df=1", "df=2", "df=5", "df=10", "df=20"), 
        bty = "n", col = 1:5, lty = 1:5)
    abline(h = 0)
    readline("hit return\n")
    x = seq(-5, 5, 0.01)
    dfs = c(1, 2, 5, 10, 20, 30)
    plot(x, dnorm(x), xlab = "t", ylab = "density", type = "l")
    i = 1
    for (df in dfs) {
        i = i + 1
        lines(x, dt(x, df), col = i, lty = i)
    }
    legend(-5, 0.4, expression("df=1", "df=2", "df=5", "df=10", 
        "df=20", "df=30", "df=" ~ infinity), bty = "n", col = c(2:7, 
        1), lty = c(2:7, 1))
    abline(h = 0)
    readline("hit return\n")
    x = seq(0.01, 5, 0.01)
    dfs1 = c(1, 2, 5, 10, 20, 50)
    dfs2 = c(3, 5, 5, 20, 20, 100)
    i = 1
    plot(x, df(x, dfs1[i], dfs2[i]), type = "l", xlab = "F", 
        ylab = "density", ylim = c(0, 1.7))
    for (i in 2:6) {
        lines(x, df(x, dfs1[i], dfs2[i]), lty = i, col = i)
    }
    abline(h = 0)
    legend(2, 1.5, paste("df1 =", dfs1, ", df2 =", dfs2), col = 1:6, 
        lty = 1:6, bty = "n")
    readline("hit return\n")
    x = seq(-5, 15, 0.01)
    deltas = c(1, 2, 4)
    plot(x, dt(x, df = 6), xlab = "t", ylab = "density", type = "l")
    abline(h = 0)
    for (i in 2:4) {
        lines(x, dt(x, df = 6, deltas[i - 1]), col = i, lty = i)
    }
    legend(7, 0.35, paste("df = 6, nct =", c(0, deltas)), bty = "n", 
        lty = 1:4, col = 1:4)
}