### WFF

 LA home Computing Logic  Prop'l   Wff

Type a boolean expression (identifiers, parentheses, and operators 'and', 'or', '->', 'not') in the Wff area of the HTML FORM below and press the 'go' button. Experiment.

 Wff: USE NETSCAPE 4.7 OR LATER WITH JavaScript 1.1 OR LATER, ON! L. A l l i s o n, C o m p. S c i., M o n a s h U n i, .au L.A.

Remember, there are three possible outcomes: A Wff is either a tautology (always true), a contradiction (always false), or satisfiable (sometimes true, sometimes false).

### Exercises

1. What kind of Wff leads to the greatest expansion when it is converted into CNF?
2. Ditto DNF?
3. Some advertising relies on the following kind of "reasoning":
People who are (rich | powerful | attractive | etc.) buy XXX, therefore if you buy XXX you will become (rich | powerful | attractive | etc.).
• Is this kind of "reasoning" valid?
• Consider: People who are [whatever] buy food;
• Formulate the advertising "reasoning" as a Wff and use the FORM to see the true situation.
4. Give a related but different kind of reasoning with a different outcome.

### Notes

• Read the [propositional logic] page to learn more about the algorithm used on the HTML FORM above.
• The programming language Prolog is based on the more powerful Predicate Logic. There is a demonstration Prolog interpreter [here...].
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