Predicate Logic / changing the result of a statement by asking statment? Let's have a simple statement that P:(x) is false It's good weather today. (it's not) But by evoking the statement, the result can change. Is there something in any field of Mathematics that describe this case? Or it's completely out of rules? I'm sure that my question is not exact, i'm open to any correction. Thanks.

Have a look at this answer.

If you take a tensed view of things, there is, quite clearly, no problem (you only need to check the truth value before evocation of the statement). However, this view is not taken in mathematics often; a tenseless view cannot allow for a statement which changes the truth value that it states. You may declare any such statement whose truth value depends on evocation or temporality to arbitrarily be false by convention.