@article{SF_1986__34_134830,
     author = {J. Leech},
     title = {The ...-category of a monoid.},
     journal = {Semigroup forum},
     pages = {89--116},
     publisher = {mathdoc},
     volume = {34},
     year = {1986},
     zbl = {0612.20035},
     url = {http://geodesic.mathdoc.fr/item/SF_1986__34_134830/}
}