Mackaay, Marco2018-12-072018-12-071999-050001-8708http://hdl.handle.net/10400.1/11726engHigher-dimensional algebraState-Sum invariantsQuantum-field theoryCategories3-ManifoldsCohomologySpherical 2-categories and 4-manifold invariantsjournal article10.1006/aima.1998.1798