From lliao@ren.eecis.udel.edu Wed Nov 27 22:55:00 2002
Date: Wed, 27 Nov 2002 22:53:32 -0500 (EST)
From: Li Liao <lliao@ren.eecis.udel.edu>
To: natasha <natasha@udel.edu>
Subject: Re: subtypes




> I found very little info on subtypes in our book. And there is nothing on three ways of subtyping there(extension, covariant and contravariant). I read all chapter 10 and didn't find anything. What chapter is it?
> Thank you.
>

You are right, the textbook does not talk much about subtyping.
In additional to the lecture notes, you may refer to the following
papers for more detailed discussions on subtyping.

1. Cardelli and Wegner, "On Understanding Types, ...", pp 30-31,
section 6.1.

2. Cardelli, "Type Systems", pp28, section 6.

I have put electronic copy of these two papers on the tentative schedule
page as non required readings.

I hope this is helpful.

Li