Nonisomorphic Gassmann equivalent regular subgroups
ID: nonisomorphic-gassmann-equivalent-regular-subgroups
For an odd prime , embed the elementary abelian group and the Heisenberg group over a prime field regularly in . Every nonidentity element has order and hence regular permutation cycle type . The two subgroups have equal intersection counts with every symmetric-group conjugacy class, so they are Gassmann equivalent, but they are not isomorphic because one is abelian and the other is not. Using a compact simply connected isometric cover with ambient deck group gives quotients with these nonisomorphic fundamental groups; Sunada theorem makes them isospectral while their topology differs.
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