On limits of fractional Orlicz-Sobolev seminorms

We establish versions for fractional Orlicz-Sobolev seminorms, built upon Young functions, of the Bourgain-Brezis-Mironescu theorem on the limit as s->1^-, and of the Maz'ya-Shaposhnikova theorem on the limit as s-> 0^+ , dealing with classical fractional Sobolev spaces. As regards the limit as s->1^-, Young functions with an asymptotic linear growth are also considered in connection with the space of functions of bounded variation. Concerning the limit as s-> 0^+, Young functions fulfilling the \Delta_2-condition are admissible. Indeed, counterexamples show that our result may fail if this condition is dropped. This is a joint work with Andrea Cianchi, Lubos Pick and Lenka Slavikova.