@article{PORMA_1967__26_2_115011,
     author = {Magill, Kenneth D. jr.},
     title = {Subgroups of semigroups of functions},
     journal = {Portugaliae mathematica},
     pages = {133--147},
     year = {1967},
     volume = {26},
     number = {2},
     mrnumber = {0263057},
     zbl = {0174.04404},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1967__26_2_115011/}
}