τ-invariants for knots in rational homology spheres

Ozsvath and Szabo used the knot filtration on (CF) over cap (S-3) to define the tau-invariant for knots in the 3-sphere. We generalize their construction and define a collection of tau- invariants associated to a knot K in a rational homology sphere Y. We then show that some of these invariants provide lower bounds for the genus of a surface with boundary K properly embedded in a negative definite 4 - manifold with boundary Y.