# From almost optimal algorithms to logics for complexity classes via listings and a halting problem

Presented by:
Y Chen Shanghai Jiao Tong University
Date:
Thursday 29th March 2012 - 09:00 to 10:00
Venue:
INI Seminar Room 1
Abstract:
Let $C$ denote one of the complexity classes polynomial time,'' logspace,'' or nondeterministic logspace.'' We introduce a logic $L(C)_{\mathrm{inv}}$ and show generalizations and variants of the equivalence ($L(C)_{\mathrm{inv}}$ captures $C$ if and only if there is an almost $C$-optimal algorithm in $C$ for the set TAUT of tautologies of propositional logic.) These statements are also equivalent to the existence of a listing of subsets in $C$ of TAUT by corresponding Turing machines and equivalent to the fact that a certain parameterized halting problem is in the parameterized complexity class $\mathrm{XC}_{\rm uni}$.
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