  We derive a cut-and-paste surgery formula of Seiberg--Witten invariants for
negative definite plumbed rational homology 3-spheres. It is similar to (and
motivated by) Okuma's recursion formula [arXiv:math.AG/0610464, 4.5] targeting
analytic invariants of splice quotient singularities. The two formulas combined
provide automatically a proof of the equivariant version
[arXiv:math.AG/0310084, 5.2(b)] of the `Seiberg--Witten invariant conjecture'
[arXiv:math.AG/0111298] for these singularities.
