We study Koszul homology over Gorenstein rings. If an ideal is strongly
Cohen-Macaulay, the Koszul homology algebra satisfies Poincar\'e duality. We
prove a version of this duality which holds for all ideals and allows us to
give two criteria for an ideal to be strongly Cohen-Macaulay. The first can be
compared to a result of Hartshorne and Ogus; the second is a generalization of
a result of Herzog, Simis, and Vasconcelos using sliding depth.
This paper concerns the question of whether a more direct limit can be used
to obtain the limit Hilbert Kunz multiplicity, a possible candidate for a
characteristic zero Hilbert-Kunz multiplicity. The main goal is to establish an
affirmative answer for one of the main cases for which the limit Hilbert Kunz
multiplicity is even known to exist, namely that of graded ideals in the
homogeneous coordinate ring of smooth projective curves.