Bogolyubov, N. N., and A. K. Prykarpatsky. 2007. “Generalized De Rham-Hodge Complexes, the Related Characteristic Chern Classes, and Some Applications to Integrable Multidimensional Differential Systems on Riemannian Manifolds”. Ukrains’kyi Matematychnyi Zhurnal 59 (3), 327–344. https://umj.imath.kiev.ua/index.php/umj/article/view/3310.