schurLevel -- Number of SchurRings the ring is a tensor product of.

For the representation ring R of a product of lev general linear and/or symmetric groups, the function returns lev. If R is not a representation ring, the function returns 0.

A three-level tower mixing GL-factors with an S_n-factor counts each layer, regardless of which group is acting:

A Symmetric ring (produced by symmetricRing) sits over a single tower slot and reports schurLevel equal to 1, while an ordinary polynomial ring or the base field report 0: