  We prove that the combinatorial side of the "Rational Shuffle Conjecture"
provides a Schur-positive symmetric polynomial. Furthermore, we prove that the
contribution of a given rational Dyck path can be computed as a certain skew
LLT polynomial, thus generalizing the result of Haglund, Haiman, Loehr, Remmel
and Ulyanov. The corresponding skew diagram is described explicitly in terms of
a certain (m,n)-core.
