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According to Widgersen, et. al. http://www.cs.huji.ac.il/~nati/PAPERS/expander_survey.pdf, the statement is a bit different. The right hand side could read ${\displaystyle \lambda {\sqrt {|S|\cdot |T|}}\,.}$ BumblingMathematician ( talk) 01:54, 9 March 2013 (UTC) reply

This is because the eigenvalues are normalized in a different way. In Expander_graph and apparently in this article, too, the largest eigenvalue is 1, and in Hoory et al. all eigenvalues are larger by a factor of d. ylloh ( talk) 18:01, 10 March 2013 (UTC) reply

Since when do we use bra and ket notation for matrices in combinatorics? 178.38.179.63 ( talk) 10:47, 11 December 2014 (UTC) reply