  We compare the sheaf-theoretic and singular chain versions of Poincare
duality for intersection homology, showing that they are isomorphic via
naturally defined maps. Similarly, we demonstrate the existence of canonical
isomorphisms between the singular intersection cohomology cup product, the
hypercohomology product induced by the Goresky-MacPherson sheaf pairing, and,
for PL pseudomanifolds, the Goresky-MacPherson PL intersection product. We also
show that the de Rham isomorphism of Brasselet, Hector, and Saralegi preserves
product structures.
