@article{JEMS_2013_15_6_a11,
     author = {Richard J. Gardner and Daniel Hug and Wolfgang Weil},
     title = {Operations between sets in geometry},
     journal = {Journal of the European Mathematical Society},
     pages = {2297--2352},
     publisher = {mathdoc},
     volume = {15},
     number = {6},
     year = {2013},
     doi = {10.4171/jems/422},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/jems/422/}
}