Abstract:
We study the function Λm(X), 0<m<1, of compact sets X in Rn, n⩾2, defined as the distance in the space Cm(X)≡lipm(X) from the function |x|2 to the subspace Hm(X) which is the closure in Cm(X) of the class of functions harmonic in the neighborhood of X (each function in its own neighborhood). We prove the equivalence of the conditions Λm(X)=0 and Cm(X)=Hm(X). We derive an estimate from above that depends only on the geometrical properties of the set X (on its volume).
Citation:
Yu. A. Gorokhov, “Approximation by harmonic functions in the Cm-Norm and harmonic Cm-capacity of compact sets in Rn”, Mat. Zametki, 62:3 (1997), 372–382; Math. Notes, 62:3 (1997), 314–322