%0 Journal Article %A J. Reunsumrit %A T. Sitthiwirattham %T A New Class of Four-Point Fractional Sum Boundary Value Problems for Nonlinear Sequential Fractional Difference Equations Involving Shift Operators %J Kragujevac Journal of Mathematics %D 2018 %P 371 %V 42 %N 3 %I mathdoc %U http://geodesic.mathdoc.fr/item/KJM_2018_42_3_a4/ %G en %F KJM_2018_42_3_a4