  We connect twisted vertex operator presentation of Hall-Littlewood
polynomials with the action of charged free fermions, describe a boson-fermion
correspondence that relates twisted vertex operators with classical Heisenberg
algebra. We also show that the elements of the orthogonal to Schur functions
basis of the one-parameter deformation of the ring of symmetric functions
$\Lambda[t]$ are $\tau$-functions of KP hierarchy.
