Labs should be in PDF format with all figures, code, and any other materials included. The filename should follow the recipe lab#_(lastname)(firstinitial).pdf. The labs are due at the beginning of the next lab at the latest.
file was producing funky pictures for different values of D (not showing the 1-1 line, for instance) but has been updated. If the plot you're getting by calling cobweb is making you sad, redownload the file and try running your code again.
The lab currently says the way to add labels to your plot is title(main='title', xlab='your x label', ylab='your y label')
but this actually is a pretty bad way (since it makes an ugly overlay over the previous labels). Instead, when you originally plot, try
plot(x,y, xlab='your x label', ylab='your y label')
. You'll get much prettier results.