1. E. M. Patterson and A. G. Walker, “Riemannian extensions,” Quant. J. Math., 3, 19–28 (1952).
2. K. Yano and Sh. Ishihara, “Tangent and cotangent bundles: Differential geometry,” Pure Appl. Math., No. 16 (1973).
3. V. Dryuma, “On Riemannian extension of the Schwarzschild metric,” Bull. Acad. Şti. Rep. Mold. Mat., No. 3, 92–103 (2003).
4. V. Dryuma, “The Riemannian extension in theory of differential equations and their application,” Mat. Fiz. Anal. Geom., 10, No. 3, 307–325 (2003).
5. G. T. Ganchev and A. V. Borisov, “Note on the almost complex manifolds with a Norden metric,” C. R. Acad. Bulg. Sci., 39, No. 5, 31–34 (1986).