@article{SF_1979__18_134365,
     author = {K.D. jr. Magill and B.B. Baird},
     title = {Green's ...-relation and climbing mountains.},
     journal = {Semigroup forum},
     pages = {347--370},
     publisher = {mathdoc},
     volume = {18},
     year = {1979},
     zbl = {0431.20051},
     url = {http://geodesic.mathdoc.fr/item/SF_1979__18_134365/}
}