@article{CM_1980__42_3_391_0,
     author = {Sierksma, Gerard},
     title = {Convexity on unions of sets},
     journal = {Compositio Mathematica},
     pages = {391--400},
     publisher = {Sijthoff et Noordhoff International Publishers},
     volume = {42},
     number = {3},
     year = {1980},
     mrnumber = {607378},
     zbl = {0454.52001},
     language = {en},
     url = {http://www.numdam.org/item/CM_1980__42_3_391_0/}
}