due February 10th, 1999

INSTRUCTIONS: This assignment is due February 10th 1999, in class. Groups may hand in a single assignment paper. The maximum group size is 4.

The assignments must have the name and York number of all group members listed at the top of the paper.

Any axiom may be used. Lower numbered theorems may be used in the proof of a higher numbered theorem.

- Give a full dress proof that . You may use Theorems upto and including 3.64.
SOLUTION:

By TRANSITIVITY 4 times we have that .

- Give a full dress proof of modus ponens ( 3.77), i.e. .
SOLUTION:

We have that . Leib with E being gives that . Now , and Sim Subs with

*p*,*q*:=*q*,*p*gives that . Hence by EQUANIMITY we have that .So , and , so by EQUANIMITY it follows that .