@article{SF_1971__3_133859,
     author = {K.D. jr. Magill and S. Yamamuro},
     title = {Union and symmetry preserving homomorphisms of semigroups of closed relations.},
     journal = {Semigroup forum},
     pages = {168--172},
     publisher = {mathdoc},
     volume = {3},
     year = {1971},
     zbl = {0247.20075},
     url = {http://geodesic.mathdoc.fr/item/SF_1971__3_133859/}
}