  The dual stable Grothendieck polynomials are a deformation of the Schur
functions, originating in the study of the K-theory of the Grassmannian. We
generalize these polynomials by introducing a countable family of additional
parameters, and we prove that this generalization still defines symmetric
functions. For this fact, we give two self-contained proofs, one of which
constructs a family of involutions on the set of reverse plane partitions
generalizing the Bender-Knuth involutions on semistandard tableaux, whereas the
other classifies the structure of reverse plane partitions with entries 1 and
2.
