Hefter, S. L., and A. B. Goncharuk. 2022. “Linear Differential Equation With Inhomogeneity in the Form of a Formal Power Series over a Ring With Non-Archimedean Valuation”. Ukrains’kyi Matematychnyi Zhurnal 74 (11): 1463-77. https://doi.org/10.37863/umzh.v74i11.7287.