This is VALID.
Notice how application of the rule removes two adjacent snakes from a complete formula, not just part of a formula.
The correct application of the rule adds or removes two adjacent tildes ("snakes," "negation signs," whatever) to a complete formula.
Before you go back to the reading, consider the following two attempts to apply NN. Are they both good? Both bad? Or what?
Use your browsers "back" key to return.
This Site is Proudly Hosted By: