Audrito, A., Felipe-Navarro, J.-C. ., & Ros-Oton, X. . (2023). The Neumann problem for the fractional Laplacian: regularity up to the boundary. ANNALI SCUOLA NORMALE SUPERIORE - CLASSE DI SCIENZE, 24(2), 1155-1222. https://doi.org/10.2422/2036-2145.202105_096