@article{MAN_1974__208_162568,
     author = {Paul Georgiou},
     title = {A {Semigroup} {Structure} in the {Space} of {Liftings.}},
     journal = {Mathematische Annalen},
     pages = {195--202},
     publisher = {mathdoc},
     volume = {208},
     year = {1974},
     zbl = {0302.46033},
     url = {http://geodesic.mathdoc.fr/item/MAN_1974__208_162568/}
}