[1] Epstein D. B.: Natural tensors on Riemannian manifolds. J. Differential Geom. 10 (1975), 631-645. MR 0415531 | Zbl 0321.53039

[2] Krupka D., Mikolášová V.: On the uniqueness of some differential invariants: $d, [ , ], {\nabla}$. Czechoslovak Mathematical Journal 34 (109) (1984), 588-597. MR 0764440

[3] Mikulski W. M.: Classification theorem for F-metrices. to appear.

[4] Nijenhuis A.: Natural bundles and their general properties. in "Differential Geometry, in honour of K. Yano," Tokio, 1972, pp. 317-334. MR 0380862 | Zbl 0246.53018