A bstract We propose a concrete form of a vertex function, which we call O-vertex, for the
intersection between an O5-plane and a 5-brane in the topological vertex formalism, as an
extension of the work of [1]. Using the O-vertex it is possible to compute the Nekrasov
partition functions of 5d theories realized on any 5-brane web diagrams with O5-planes. We
apply our proposal to 5-brane webs with an O5-plane and compute the partition functions of
pure SO (N) gauge theories and the pure G 2 gauge theory. The obtained results agree with …

We propose a concrete form of a vertex function, which we call O-vertex, for the intersection
between an O5-plane and a 5-brane in the topological vertex formalism, as an extension of
the work of [1]. Using the O-vertex it is possible to compute the Nekrasov partition functions
of 5d theories realized on any 5-brane web diagrams with O5-planes. We apply our
proposal to 5-brane webs with an O5-plane and compute the partition functions of pure SO
(N) gauge theories and the pure G 2 gauge theory. The obtained results agree with the …