  We study the Felderhof free-fermion six-vertex model, whose wavefunction
recently turned out to possess rich combinatorial structure of the Schur
polynomials. We investigate the dual version of the wavefunction in this paper,
which seems to be a harder object to analyze. We evaluate the dual wavefunction
in two ways. First, we give the exact correspondence between the dual
wavefunction and the Schur polynomials, for which two proofs are given. Next,
we make a microscopic analysis and express the dual wavefunction in terms of
strict Gelfand-Tsetlin pattern. As a consequence of these two ways of
evaluation of the dual wavefunction, we obtain a dual version of the Tokuyama
combinatorial formula for the Schur polynomials. We also give a generalization
of the correspondence between the dual wavefunction of the Felderhof model and
the factorial Schur polynomials.
