This is INVALID.
See how two snakes have been removed from part of a formula. This is not allowed by the rule.
The correct application of the rule adds or removes two adjacent negation signs ("tildes," "snakes," whatever.) to a complete formula. There is no rule that allows alterations to just part of a 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: