El-Sayed, Ahmed, and Reda Gamal. “Infinite Point and Riemann–Stieltjes Integral Conditions for an Integro-Differential Equation”. Nonlinear Analysis: Modelling and Control, vol. 24, no. 5, Sept. 2019, pp. 733–754, https://doi.org/10.15388/NA.2019.5.4.