S5 (modal Logic)
In logic and philosophy, S5 is one of five systems of modal logic proposed by Clarence Irving Lewis and Cooper Harold Langford in their 1932 book Symbolic Logic. It is a normal modal logic, and one of the oldest systems of modal logic of any kind.
Other articles related to "s5":
... http/home.utah.edu/nahaj/logic/structures/systems/s5html http/www.columbia.edu/av72/modallogic/LectureNotes/ModalLogic06.pdf ...