“…The fractional Sobolev spaces with variable exponents were first introduced recently by Kaufmann, Rossi, and Vidal [
43], and have been studied in different contexts. See [
4, 6–15, 19, 25, 39, 40, 50, 55] and references therein. Note that the Triebel–Lizorkin spaces with variable smoothness and integrability have been introduced in [
30], which are isomorphic to
if
, respectively, the variable exponent Bessel potential space
for
under suitable assumptions on p .…”