  We study the system of equations of motion for inextensible strings. This
system possesses many internal symmetries, and is related to discontinuous
systems of conservation laws and the total variation wave equation. We prove
existence of generalized Young measure solutions with non-negative tension
after transforming the problem into a system of conservation laws and
approximating it with a regularized system for which we obtain uniform
estimates of the energy and the tension. We also discuss sufficient conditions
for non-negativity of the tension for strong solutions.
