Vector hyperbolic equations on the sphere possessing integrable third order symmetries

The complete lists of vector hyperbolic equations on the sphere that have integrable third order vector isotropic and anisotropic symmetries are presented. Several new integrable hyperbolic vector models are found. By their integrability we mean the existence of vector Backlund transformations depending on a parameter. For all new equations such transformations are constructed.
Comment: Submitted in Lett. Math. Phys