weaker version of the corresponding ◊S; it was introduced in 1975 by AdamOstaszewski. For a given cardinal number κ {\displaystyle \kappa } and a stationary
Piotr Ostaszewski (born 5 April 1964, Żyrardów) is a Polish historian, political scientist and translator. From 2017 to 2024 he served as an ambassador
and head of Jagiellonian University and another AdamOstaszewski was President of Plock until 1934. Adam Hrebnicki-Doktorowicz (1857–1941) was a professor
(reprint of 1959[3] and 1971 Springer-Verlag ed.), Springer-Verlag. Ostaszewski, Adam (1990). Advanced mathematical methods. Cambridge; New York: Cambridge