On Wednesday, December 5, **Torben Brauner** will give a LIRa-affiliated lunch talk.

Everyone is cordially invited! Since the talk will be during lunch time, you can bring lunch and eat during the talk.

**Speaker:** Torben Brauner (Roskilde University)

**Title:** Hybrid-Logical Proof-Theory: With an Application to Reasoning in False-Belief Tasks

**Room:** Science Park 904, room D1.115

**Time:** Wednesday, 5 December, 12:00-13:00

**Abstract: **Hybrid logic is an extension of ordinary modal logic which allows explicit reference to individual points in a model (where the points represent times, possible worlds, states in a computer, or something else). This additional expressive power is useful for many applications, for example when reasoning about time one often wants to formulate a series of statements about what happens at specific times.

There is little consensus about proof-theory for ordinary modal logic. Many modal-logical proof systems lack important properties and the relationships between proof systems for different modal logics are often unclear. In my talk I will demonstrate that these deficiencies are remedied by hybrid-logical proof-theory.

In my talk I first give a brief introduction to hybrid logic and its origin in Arthur Prior’s temporal logic. I then describe essential proof-theoretical results for natural deduction formulations of hybrid logic. Finally, I show how a proof system for hybrid logic can be used to formalize what are called false-belief tasks in cognitive psychology.