Asking systolic questions often stimulates questions in related fields. Thus, a notion of "systolic category" of a manifold has been defined and investigated, exhibiting a connection to the Lusternik–Schnirelmann category (LS category). Note that the systolic category (as well as the LS category) is, by definition, an integer. The two categories have been shown to coincide for both surfaces and 3-manifolds. Moreover, for orientable 4-manifolds, systolic category is a lower bound for LS category. Once the connection is established, the influence is mutual: known results about LS category stimulate systolic questions, and vice versa.