Title: Time Travel: Time Structure with cycles

Speaker:   Liqing Ruan (PKU)

Time: 15:10 ~ 18:00  (Jun. 6th)

Location: Room 501, No.2 Teaching Building

Abstract: In this talk, I will focus on the topic of time travel, introduce some models with cycles and semantics on them. About "time travel", we will discuss some specific examples from fiction such as interstellar, back to future, Avengers, tenet and try to give a definition. Then we will discuss   problems that appear if we could travel in time, for instant, grandfather paradox. About semantics, I would like to introduce ideas in "Cycle detection in computation tree logic(2018)" by F. Gaëlle and some of my own ideas. The point is that we introduce a new modality \diamonddot to describe properties in a cyclic time structure. Besides, the logic with new modalities does not have the finite-model property, tree-model property, and it is not invariant under bisimulation, but it is invariant under a \diamonddot version of bisimulation.