@article{10_2140_agt_2001_1_491,
     author = {Roitberg, Joseph},
     title = {The product formula for {Lusternik{\textendash}Schnirelmann} category},
     journal = {Algebraic and Geometric Topology},
     pages = {491--502},
     year = {2001},
     volume = {1},
     number = {1},
     doi = {10.2140/agt.2001.1.491},
     url = {http://geodesic.mathdoc.fr/articles/10.2140/agt.2001.1.491/}
}