  A recent paper of Bump, McNamara and Nakasuji introduced a factorial version
of Tokuyama's identity, expressing the partition function of a six vertex model
as the product of a t-deformed Vandermonde and a Schur function. Here we
provide an extension of their result by exploiting the language of primed
shifted tableaux, with its proof based on the use of non-intersecting lattice
paths.

Combinatorics