Samoilenko , A. M., and P. F. Samusenko. “Asymptotic Integration of Singularly Perturbed Differential-Algebraic Equations With Turning Points. II”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 73, no. 6, June 2021, pp. 849 -64, doi:10.37863/umzh.v73i6.6260.