  We give formulas for the extension groups between tautological sheaves and
more general between tautological objects twisted by a determinant line bundle
on the Hilbert scheme of points on a smooth quasi-projective surface. We do
this using L. Scala's results about the image of tautological sheaves under the
Bridgeland-King-Reid equivalence. We also compute the Yoneda products in terms
of these formulas.
