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\title{Parikh's theorem}
\author{Fabian Lehr}
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\begin{abstract}
In formal language theory, the \emph{Parikh image} of a language $L$
is the set of multisets of the words in $L$: the order of letters
becomes irrelevant, only the number of occurrences is relevant.
Parikh's Theorem states that the Parikh image of a context-free
language is the same as the Parikh image of some regular language.
This formalization closely follows Pilling's proof \cite{Pilling}:
It describes a context-free language as a minimal solution to a
system of equations induced by a context free grammar for this
language. Then it is shown that there exists a minimal solution
to this system which is regular, such that the regular solution and the
context-free language have the same Parikh image.
\end{abstract}
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