System of Non-Linear Volterra Integral Equations in a Direct-Sum of Hilbert Spaces. J. Nig. Soc. Phys. Sci. [Internet]. 2022 Oct. 1 [cited 2024 Apr. 27];4(4):1021. Available from: https://www.journal.nsps.org.ng/index.php/jnsps/article/view/1021