@article{MM2_1983__42_154921,
     author = {Luis Montejano},
     title = {A {Quick} proof of {Singhof's} cat {(M} x {S1)} = cat {(M)} + 1 theorem.},
     journal = {Manuscripta mathematica},
     pages = {49--52},
     publisher = {mathdoc},
     volume = {42},
     year = {1983},
     zbl = {0639.55001},
     url = {http://geodesic.mathdoc.fr/item/MM2_1983__42_154921/}
}