Background: Murray Bookchin (January 14, 1921 - July 30, 2006) was an American social theorist, author, orator, historian, and political philosopher. A pioneer in the ecology movement, Bookchin formulated and developed the theory of social ecology within anarchist, libertarian socialist, and ecological thought. He was the author of two dozen books covering topics in politics, philosophy, history, urban affairs, and ecology. Among the most important were Our Synthetic Environment (1962), Post-Scarcity Anarchism (1971) and The Ecology of Freedom (1982).
Context: Though Bookchin, by his own recognition, failed to win over a substantial body of supporters during his own lifetime, his ideas have nonetheless influenced movements and thinkers across the globe.  Notable among these is the Kurdistan Workers' Party (PKK), an organisation in Turkey which has fought the Turkish state since the 1980s to try to secure greater political and cultural rights for the country's Kurds. Though founded on a rigid Marxist-Leninist ideology, the PKK has seen a shift in its thought and aims since the capture and imprisonment of its leader, Abdullah Ocalan, in 1999. Ocalan began reading a variety of post-Marxist political theory while in prison, and found particular currency in Bookchin's works.  Ocalan attempted in early 2004 to arrange a meeting with Bookchin through his lawyers, describing himself as Bookchin's "student" eager to adapt his thought to Middle Eastern society. Bookchin was too ill to accept the request. In May 2004 Bookchin conveyed this message "My hope is that the Kurdish people will one day be able to establish a free, rational society that will allow their brilliance once again to flourish. They are fortunate indeed to have a leader of Mr. Ocalan's talents to guide them". When Bookchin died in 2006, the PKK hailed the American thinker as "one of the greatest social scientists of the 20th century", and vowed to put his theory into practice.  "Democratic Confederalism", the variation on Communalism developed by Ocalan in his writings and adopted by the PKK, does not outwardly seek Kurdish rights within the context of the formation of an independent state separate from Turkey. The PKK claims that this project is not envisioned as being only for Kurds, but rather for all peoples of the region, regardless of their ethnic, national, or religious background. Rather, it promulgates the formation of assemblies and organisations beginning at the grassroots level to enact its ideals in a non-state framework beginning at the local level. It also places a particular emphasis on securing and promoting women's rights. The PKK has had some success in implementing its programme, through organisations such as the Democratic Society Congress (DTK), which coordinates political and social activities within Turkey, and the Koma Civaken Kurdistan (KCK), which does so across all countries where Kurds live.
Question: What was Bookchin sick with?

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