\begin{Schunk}
\begin{Sinput}
 x <- seq(-4,4, length.out=1000)
 px1 <- dt(x, df=1)
 px2 <- dt(x, df=5)
 px3 <- dt(x, df=20)
 px4 <- dt(x, df=100)
 plot(x, px1, xlab="t",ylab="probability density of t",type="l", ylim=c(0,0.5))
 lines(x,px2, lty=2)
 lines(x,px3, lty=3)
 lines(x,px4, lty=4)
 legend("topright",legend=c("df=1","df=5", "df=20", "df=100"),lty=1:4)
\end{Sinput}
\end{Schunk}
