Generalized triangle groups, expanders, and a problem of Agol and Wise


الملخص بالإنكليزية

Answering a question asked by Agol and Wise, we show that a desired stronger form of Wises malnormal special quotient theorem does not hold. The counterexamples are generalizations of triangle groups, built using the Ramanujan graphs constructed by Lubotzky--Phillips--Sarnak.

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