Variational principles for magnetohydrodynamics were introduced by previous authors both in Lagrangian and Eulerian form. In a previous work [1] Yahalom & Lynden-Bell introduced a simpler Eulerian variational principle from which all the relevant equations of magnetohydrodynamics can be derived. The variational principles were given in terms of six independent functions for non-stationary flows and three independent functions for stationary flows. This is less than the seven variables which appear in the standard equations of magnetohydrodynamics which are the magnetic field B the velocity field V and the density. In a more recent work [2] the number of needed functions was further reduced and it was shown that magnetohydrodynamics is mathematically equivalent to a four function field theory defined a by a Lagrangian. The four functions include two surfaces whose intersections consist the magnetic field lines, the part of the velocity field not defined by the commoving magnetic field and the density. The Lagrangian admits a newly discovered group of Diffeomorphism Symmetry.