На 26 ноември 2021 г. (петък) от 13:00 часа ще се проведе дистанционно заседание на семинара по „Алгебра и логика”. Доклад на тема On a method of proving the non-existence of modal formulae satisfying certain syntactic properties and defining a given class of frames ще изнесе Петър Илиев (ИФС-БАН и ИМИ-БАН). Абстракт. We elaborate on semantically labeled syntax trees, which provide a method of proving the non-existence of modal formulae satisfying certain syntactic properties and defining a given class of either models or frames, and use them to show that there are classes of Kripke frames that are definable by both non-Sahlqvist and Sahlqvist formulae but the latter require more propositional variables. The talk is based on the following articles. P. Iliev. On a method [...]