Samoilenko , A. M., and P. F. Samusenko. “Asymptotic Integration of Singularly Perturbed Differential Algebraic Equations With Turning Points. Part I”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 72, no. 12, Dec. 2020, pp. 1669-81, doi:10.37863/umzh.v72i12.6261.