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IPC classification navigator
https://ipcpub.wipo.int/?notion=scheme&version=20220101&symbol=none&menulang=en&lang=en&viewmode=f&fipcpc=no&showdeleted=yes&indexes=no&headings=yes¬es=yes&direction=o2n&initial=A&cwid=none&tree=no&searchmode=smart
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Patent Pending — Bicycle technology
http://patentpending.blogs.com/patent_pending_blog/bicycle_technology/index.html
Lots of interesting stuff here about the history of technology; I'm mostly interested in the bikes though