  In [DKO] we constructed virtual fundamental classes $[[ Hilb^m_V ]]$ for
Hilbert schemes of divisors of topological type m on a surface V, and used
these classes to define the Poincare invariant of V:
  (P^+_V,P^-_V): H^2(V,Z) --> \Lambda^* H^1(V,Z) x \Lambda^* H^1(V,Z)
  We conjecture that this invariant coincides with the full Seiberg-Witten
invariant computed with respect to the canonical orientation data.
  In this note we prove that the existence of an integral curve $C \subset V$
induces relations between some of these virtual fundamental classes $[[Hilb^m_V
]]$. The corresponding relations for the Poincare invariant can be considered
as algebraic analoga of the fundamental relations obtained in [OS].
