Formulas expressing totally nonstable truth values of formulas

In this short paper we consider problem of nonstable truth values of formulas. We investigate temporal-modal logic for description of reliability information. The logic itself is generated by rather standard models on linear time. We consider intervals of nonstable truth values of formulas. This mean that the formula permanently and for a reasonably big time change its truth from true to false and vice versa. We aim to construct some technique and to find an algorithm which may recognize permanently nonstable formulas.