### 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.

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

- What
*kind*of Wff leads to the greatest expansion when it is converted into CNF? - Ditto DNF?
- 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.

- 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...].