Comparing nonorientable three genus and nonorientable four genus of torus knots

Stanislav Jabuka, Cornelia A. Van Cott

Published 2019-07-30Version 1

We compare the values of the nonorientable three genus (or, crosscap number) and the nonorientable four genus of torus knots. In particular, we show that the difference between these two invariants can be arbitrarily large. This contrasts with the orientable setting. Seifert proved that the orientable three genus of the torus knot T(p,q) is (p-1)(q-1)/2, and Kronheimer and Mrowka later proved that the orientable four genus of T(p,q) is also this same value.