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SUMMARY:Preservation under Substructures modulo Bounded Cores - Abhisekh S
 ankaran\, IIT Bombay
DTSTART:20120830T130000Z
DTEND:20120830T140000Z
UID:TALK39506@talks.cam.ac.uk
CONTACT:Bjarki Holm
DESCRIPTION:We investigate a model-theoretic property that generalizes the
  classical notion of preservation under substructures. We call this proper
 ty preservation under substructures modulo bounded cores\, and present a s
 yntactic characterization via $\\Sigma_2^0$ sentences for properties of ar
 bitrary structures definable by FO sentences. Towards a sharper characteri
 zation\, we show that the count of existential quantifiers in the $\\Sigma
 _2^0$ sentence equals the size of the smallest bounded core\, thus general
 izing the classical Los-Tarski theorem for sentences. We look at the notio
 n of relativizations and show its uses in establishing the sharper charact
 erization for special fragments of FO and also over special classes of str
 uctures. As a fallout of our studies\, we obtain combinatorial proofs of t
 he Los-Tarski theorem for some of the aforementioned cases. \n\n\nAbout th
 e speaker:\nThe speaker is a Ph.D. student at IIT Bombay (Mumbai\, India) 
 and is currently doing an internship at the Computer Laboratory.\n
LOCATION:Room GC22\, Computer Laboratory\, William Gates Building
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