Name of city "Doskonała Próżnia" is a joke - it translates to "Absolute Void"
Sejm is equivalent of parliament (historically it was gathering of all nobility in country, later main legislature organ).
Heweliusz on wiki: https://en.wikipedia.org/wiki/Johannes_Hevelius
@Irian "Doskonała Próżnia" is also the title of a book by the renowned Polish (sci-fi ) author Stanisław Lem, which is another joke - the book consists of reviews of non-existing books. A fitting name for an non-existing place ;]