  At densities below the neutron drip threshold, a purely elastic solid model
(including, if necessary, a frozen-in magnetic field) can provide an adequate
description of a neutron star crust, but at higher densities it will be
necessary to allow for the penetration of the solid lattice by an independently
moving current of superfluid neutrons. In order to do this, the previously
available category of relativistic elasticity models is combined here with a
separately developed category of relativistic superfluidity models in a unified
treatment based on the use of an appropriate Lagrangian master function. As
well as models of the purely variational kind, in which the vortices flow
freely with the fluid, such a master function also provides a corresponding
category of non-dissipative models in which the vortices are pinned to the
solid structure.
