@article{MM2_1991__70_1_155576,
     author = {Ulrich Knauer and Peter Normak},
     title = {Hereditary endomorphism monoids of projective acts.},
     journal = {Manuscripta mathematica},
     pages = {133--144},
     publisher = {mathdoc},
     volume = {70},
     number = {1},
     year = {1991},
     zbl = {0722.20049},
     url = {http://geodesic.mathdoc.fr/item/MM2_1991__70_1_155576/}
}