@article{10_37236_1576,
     author = {Michael E. Hoffman},
     title = {An analogue of covering space theory for ranked posets},
     journal = {The electronic journal of combinatorics},
     year = {2001},
     volume = {8},
     number = {1},
     doi = {10.37236/1576},
     zbl = {1007.06004},
     url = {http://geodesic.mathdoc.fr/articles/10.37236/1576/}
}