@article{MOMA_1991__111_1_178511,
     author = {Gerold Wagner},
     title = {On {Averaging} {Sets.}},
     journal = {Monatshefte f\"ur Mathematik},
     pages = {69--78},
     publisher = {mathdoc},
     volume = {111},
     number = {1},
     year = {1991},
     zbl = {0721.65011},
     url = {http://geodesic.mathdoc.fr/item/MOMA_1991__111_1_178511/}
}