@article{SF_1970__1_133805,
     author = {M. Mislove},
     title = {Semigroups over trees.},
     journal = {Semigroup forum},
     pages = {361--365},
     year = {1970},
     volume = {1},
     zbl = {0232.22006},
     url = {http://geodesic.mathdoc.fr/item/SF_1970__1_133805/}
}