  Using the construct of "Verdier specialization", we provide a purely
mathematical derivation of Chern class identities which upon integration yield
the D3-brane tadpole relations coming from the equivalence between F-theory and
associated weakly coupled type IIB orientifold limits. In particular, we find
that all Chern class identities associated with weak coupling limits appearing
in the physics literature are manifestations of a relative version of Verdier's
specialization formula.
