[Alta-Logic] Peripatetic seminar 15th March, 2:00pm, SS1253

[Robin Cockett]

Time: Wednesday, 2pm
Place: SS1253
Speaker: Pafal Urbaniak
Title: A four-valued decision procedure for S5

Given the basic modal language, we give a Kripkean-style semantics for a 
four-valued logic which allows to interpret the values as, respectively, 
`necessarily true', `contingently true', `contingently false', 
`necessarily false'. This yields  a table-like decision  procedure for 
the logic of this semantics. The logic generated by this account happens 
to be S5. Using the so-called  verification rule (Tarski, Lesniewski) it 
is easy to implement this procedure in PROLOG.

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Dr. Varadarajan's talks will continue his series of talks on Friday 17th March at 2pm in ICT 616 in the 
working seminar on Quillen closed model categories.

Title : Numerical Invariants in Homotopical Algebra
Abstract:
The Lusternik-Schnirelmann Category of a non empty topological space X is (n - 1) where n is the smallest number of open sets covering  X with the property that each of them is contractible in X . Thus for a contactible space the category is 0. If there is no such integer the category of X is defined to be infinity. It turned out to be an invariant of the homotopy type of X.Tudor Ganea introduced a dual invariant "Cocategory" and other invariants Nil X, Co-nil X, inductive Category etc and studied their inter-relationship. We will develop all these concepts for any object in a model category in the sense of Quillen.