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"operator theory is the branch of functional analysis which deals with bounded linear operators and their properties" --- really, only bounded? Then, why Closed operator and Densely-defined operator are in the Category:Operator theory? Boris Tsirelson (talk) 06:33, 17 April 2009 (UTC)[reply]

I added some topics, but I don't know what is most important. Please add more, and references!Brirush (talk) 04:47, 16 November 2013 (UTC)[reply]