“…For such problems, the concentration-compactness principles introduced by Lions 19,20 and its variant at infinity [21][22][23] have played a decisive role in showing a minimizing sequence or a Palais-Smale sequence is precompact. By using these concentration-compactness principles or extending them to the Sobolev spaces with fractional order or variable exponents, many authors have been successful to deal with critical problems involving p-Laplacian or p(•)-Laplacian or fractional p-Laplacian, see, for example, other studies 15,[24][25][26][27][28][29][30][31][32][33][34][35][36][37] and references therein. Recently, Ho and Kim 38 proved the concentration-compactness principles for fractional Sobolev spaces with variable exponents and obtained the existence of many solutions for a class of critical nonlocal problems with variable exponents.…”