**Victor Dalmau**

Universitat Pompeu Fabra

Constraint satisfaction problems arise in a wide variety of domains, such as combinatorics, logic, and artificial intelligence. In recent years, much effort has been directed towards classifying the complexity of all families of constraint satisfaction problems. It has been shown that it is possible to associate to every subclass of the CSP an algebra such that the complexity the corresponding CSP is completely determined by the properties of .

Let be any algebra over a finite universe. We define the *
expressiveness* of as the mapping
that given a natural number returns the number
subuniverses of . Some algebras that lead to tractable
cases of the CSP such as Mal'tsev algebras, or algebras containing a
near-unanimity operations among their term operations, satisfy the following
property:
, for some polynomial . We
call any such algebra *polynomially expressible*. We conjecture that all
polynomially expressible algebras give rise to families of constraint
satisfaction problems solvable in polynomial time. In this talk we shall
present some initial results in this direction.

2005-05-23