Many works combine elements of both utopias and dystopias. Some pirate havens were supposed to have formed anarchist societies called pirate utopias. Mannheim is most well known for his study and analysis of ideologies and utopias. In this world neither liberal nor Marxist utopias are any longer believed in. Utopias imagined by male authors have generally included equality between sexes, rather than separation. Another subgenre is "feminist utopias" and the overlapping category of feminist science fiction. Feminist utopias are a form of advocacy. Ecological utopias may advocate a society that is more sustainable. The boy quickly learns the regions are manifestations of those citizens' personal utopias. In 2001 his work was published in the book, "Crypto Anarchy, Cyberstates, and Pirate Utopias". Can we live without utopias - political, social, economic or environmental? Foucault explains the link between utopias and heterotopias using the metaphor of a mirror. Also, worth mentioning are the utopias of Metabolism, Archigram and Yona Friedman. As with many utopias, the elderly are missing. Manuel was known for his work on the history of the idea of Utopias.