Harmonic analysis in a domain with fractal boundary

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We consider the initial-boundary-value problems in a domain Ω=D×[O,T] with fractal lateral boundary S. It often occurs that an operator K on the Besov space B on the lateral boundary is bounded with respect to the Besov norms on S. We can prove the boundedness of an operator from B to B in the following method.(1)We extend a function f defined on S to R×[O,T] by using an extension operator E.(2)The Besov norm of f is estimated by the integral of |▽f(x)|×δ(x)^n over Ω, where δ(x) is the distance from x to S and n is a suitable number.(3)Instead of the boundedness of K we prove the boundedness of an operator from a function space on Ω to a function space on the outside of Ω by using the maximal functions between Ω and the outside of Ω.We proved the boundedness of an operator K, which is important to solve the Dirichlet problem by using double layer heat potentials.