Existence and Ulam–Hyers stability of nonlinear fractional differential equations via enriched (g, alpha, beta, k)-functional contractions. J. Nig. Soc. Phys. Sci. [Internet]. 2026 [cited 2026 Oct. 12];8(4):3775. Available from: https://journal.nsps.org.ng/index.php/jnsps/article/view/3775