# Are there distributions other than countable linear combinations of Dirac delta and its derivatives?

Dirac delta function is not a function in the standard sense, it is a generalized function, a distribution. Are there distributions that cannot be constructed as countable linear combinations of Dirac deltas and their derivatives?

More precisely, I am asking about existence (and examples, if applicable) of distributions $g(x)$ that are not of the following form $$g(x) = f(x) + \sum_{n=0}^\infty \sum_{k=0}^{N_n} c_{n,k} \delta^{(n)}(x-x_{n,k}),$$ where $f(x)$ is just a function in the usual sense (including step functions), $N_n \in \mathbb N_0 \cup \{\infty\}$, $c_{n,k} \in \mathbb R$, $\delta^{(n)}(x)$ is the $n$-th derivative of the Dirac delta and $x_{n,k}\in\mathbb R$.

• There is one more part in the Lebesgue decomposition of a measure. You have the first and the third. – user547557 Apr 3 '18 at 14:36

The first derivative can be identified with the so-called Cantor measure $\mu$, which assigns measure 1 to the Cantor set and measure 0 to every finite and countable set. It is singular to Lebesgue measure and to all Dirac measures.