8.3ex VI
Preparation for PD+

In each of the following problems, you are asked to show that one sentence entails another. This just means that from the first as premise, the second follows in a valid way. So, you are to derive the second from the first.

In the next section, each of these problems can be done much more easily with a new "short-cut" rule in what we'll call "PD+". However, it's important to see that this rule is not necessary. So, do these problems first just using PD. Then, after reading tutorial 8.4, come back and see how much easier these exercises are in PD+.