@article{10_4064_cm_32_1_25_37,
     author = {Carlton J. Maxson},
     title = {Semigroups of order-preserving partial endomorphisms on trees, {I}},
     journal = {Colloquium Mathematicum},
     pages = {25--37},
     publisher = {mathdoc},
     volume = {32},
     number = {1},
     year = {1974},
     doi = {10.4064/cm-32-1-25-37},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/cm-32-1-25-37/}
}