@article{SF_1971__3_133872,
     author = {U. Knauer},
     title = {Projectivity of acts and {Morita} equivalence of monoids.},
     journal = {Semigroup forum},
     pages = {359--370},
     publisher = {mathdoc},
     volume = {3},
     year = {1971},
     zbl = {0231.18013},
     url = {http://geodesic.mathdoc.fr/item/SF_1971__3_133872/}
}