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@article{SF_1974__9_134059, author = {Kenneth E. Oberhoff}, title = {Semilattice structures on trees.}, journal = {Semigroup forum}, pages = {54--73}, publisher = {mathdoc}, volume = {9}, year = {1974}, zbl = {0306.54042}, url = {http://geodesic.mathdoc.fr/item/SF_1974__9_134059/} }
Kenneth E. Oberhoff. Semilattice structures on trees.. Semigroup forum, Tome 9 (1974), pp. 54-73. http://geodesic.mathdoc.fr/item/SF_1974__9_134059/