Characterization of Closed Vector Fields in Finsler Geometry

The $\pi$-exterior derivative ${\o}d$, which is the Finslerian generalization of the (usual) exterior derivative $d$ of Riemannian geometry, is defined. The notion of a ${\o}d$-closed vector field is introduced and investigated. Various characterizations of ${\o}d$-closed vector fields are established. Some results concerning ${\o}d$-closed vector fields in relation to certain special Finsler spaces are obtained.