Scalar wave equation in a weak static gravitational fieldMankin, Romi; Piir, IvarEesti NSV Teaduste Akadeemia toimetised. Füüsika. Matemaatika = Известия Академии наук Эстонской ССР. Физика. Математика = Proceedings of Academy of Sciences of the Estonian SSR. Physics. Mathematics1983 / lk. 157-164 https://www.ester.ee/record=b1264310*est