  In the mechanics of inviscid conservative fluids, it is classical to generate
the equations of dynamics by formulating with adequate variables, that the
pressure integral calculated in the time-space domain corresponding to the
motion of the continuous medium is stationary. The present study extends this
principle to the dynamics of large deformations for isentropic motions in
thermo-elastic bodies: we use a new way of writing the equations of motion in
terms of potentials and we substitute the trace of the stress tensor for the
pressure term.
