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