The not block is located in the Logic drawer of the Blawx toolbox.
The not block is used to indicate that either the included statement is known to be false, or it cannot be proven from the facts and the rules.
The not block is a statement that can be stacked with other statements. It cannot be used in the conclusion of a rule, or in a fact block.
It accepts a single external connector, which must be a single statement.
It returns true if the connected statement is known false, or if it is not possible to prove that statement on the basis of the facts and rules.
The not block is one of two kinds of negation in Blawx, the other is the "known false" block.
The difference between them is that the known false block is true only when Blawx is certain of the falsehood of the statement. The not block is true when Blawx is certain of the falsehood, but also when Blawx is not certain of the falsehood, and can't prove the truth.
If you are not sure which negation block to use, start with "not" in rules conditions and questions.
One way to think of the difference between "known false" and "not" is by looking at the difference between "not guilty" and "innocent" in criminal law.
Courts don't typically find accused "innocent", because that would be to say that they know, as a fact, that it is not true that the party is guilty. They typically find people "not guilty", which means they may or may not be guilty, but there was not enough evidence to prove it.
If "guilty" was an attribute in Blawx, "not guilty" would be wrapping the "guilty" attribute In a "not" block, and "innocent" would be wrapping guilty in a "known false" block.