Unicorn is an attempt to unify continuum mechanics models and solvers
in the FEniCS project. We define a fundamental model for conservation
laws (mass, momentum, energy) which is fixed and then allow additional
constitutive models for stress-strain relations. The total model
(Unified Continuum formulation) is then solved using the G2 (General
Galerkin) method which is based on FEM and duality-based adaptivity.

Unicorn is initially developed from DOLFIN solver modules, for the
following equations:

    * Incompressible Navier-Stokes equations
    * Compressible Euler equations
    * ALE fluid-structure interaction
    * Lagrange elasticity

The current state of Unicorn is that Incompressible Navier-Stokes and
Lagrange elasticity have been unified in the ALE fluid-structure
interaction equation, where only the constitutive equation determines
fluid or solid.

Currently there exists 4 variants of UCSolver, one for each equation.
