Gunes, Baransel, and Musa Cakir. “A Fitted Approximate Method for Solving Singularly Perturbed Volterra–Fredholm Integro-Differential Equations With an Integral Boundary Condition”. Ukrains’kyi Matematychnyi Zhurnal, vol. 76, no. 1, Feb. 2024, pp. 115-31, https://doi.org/10.3842/umzh.v76i1.7331.