Advances in Modal Logic 15 - Paperbackby Agata Ciabattoni (Editor), David Gabelaia (Editor), Igor Sedl? r (Editor) Since ancient times, philosophers have recognised that truth comes in many 'modes', so that a proposition can be not only true or false, but also, for example, 'necessary' or 'possible'. These ideas led to the modern field of modal logic, a lively area of research at the interface of philosophy, mathematics and computer science. Nowadays, the term 'modal logic' is understood