A comprehensive review of the Pachpatte-type inequality pertaining to fractional integral operators

In the frame of fractional calculus, the term convexity is primarily utilized to address several challenges in both pure and applied research. The main focus and objective of this review paper is to present Pachpatte-type inequalities involving a variety of classes of convexities pertaining to fractional integral operators, such as h-convex, m-convex, s-convex, interval h-convex, harmonically convex, interval harmonically h-convex, LR-convex interval-valued, cr-\mathsfh-convex, n-polynomial harmonically s-type convex, ℑs-convex, (α,m)-convex, p-convex and (p,h)-convex functions. Moreover a variety of classes of preinvex functions are included, such as (s,m,ξ)-preinvex, cr-\mathsfh-preinvex, m-preinvex, n-polynomial preinvex and interval-valued functions. Included in the fractional integral operators are Riemann--Liouville fractional integral, k-Riemann--Liouville fractional integral, (k-r)-Riemann--Liouville fractional integral, Ψ-Riemann--Liouville fractional integral, fractional integral operator of exponential kernel, generalized fractional integral, Caputo-Fabrizio fractional integral, Katugampola fractional integral, conformable fractional integral, genera-lized conformable fractional integral, non-conformable fractional integral and Atangana-Baleanu fractional integral operator.