@article{MM2_1991__72_1_155647,
     author = {Karl Strambach and Martin Funk},
     title = {On free constructions.},
     journal = {Manuscripta mathematica},
     pages = {335--374},
     year = {1991},
     volume = {72},
     number = {1},
     zbl = {0739.51005},
     url = {http://geodesic.mathdoc.fr/item/MM2_1991__72_1_155647/}
}