Let $D$ be a domain of $\mathbb{R}^{m}$ and let 
$K(x)= \log|x|$ if $m=2$, and $K(x)=|x|^{2-m}$ if $m>2$. According to Riesz decomposition theorem (Hayman and Kennedy, "subharmonic functions", vol. 1, pg 104) if $u$ is subharmonic on $D$, then there is a unique Borel measure $\mu$ such that for all compact $E$ in $D$ we have
$$u(x)=\int\_{E}K(x-\zeta)d\mu(\zeta)+h(x)$$
where $h$ is harmonic on the interior
 of $E$. 


I have two questions:


1) Suppose $E$ is a compact of $D$ with no interior. Then what happens to the above formula? Does it still hold?


2) Is it true that the function $h$ is given by the integral of $u$ over the boundary of $\partial E$ of $E$ with respect to the harmonic measure?



A question about Riesz decomposition theorem
1) The formula is then meaningless: $h$ can be completely arbitrary (as there is no interior of $E$).


2) Yes, this is true. Consider a larger compact set $E'$ which is contained in $D$ and such that the interior of $E'$ contains $D$. Apply the decomposition theorem to $E'$ to get $$u(x) = \int\_{E'} K(x - \xi) d\mu(\xi) + h'(x).$$ Then $$h(x) = h'(x) - \int\_{E' \setminus E} K(x - \xi) d\mu(\xi).$$ Both $h'$ and $K(x - \xi)$ (for $\xi \in E' \setminus E$) are given as integrals with respect to the harmonic measure of $E$, and it remains to use Fubini's theorem.


