Ulrich Tamm. Size of downsets in the pushing order and a problem of Berlekamp. Discrete Applied Mathematics, 156(9):1560-1566, 2008. [doi]
@article{Tamm08-0, title = {Size of downsets in the pushing order and a problem of Berlekamp}, author = {Ulrich Tamm}, year = {2008}, doi = {10.1016/j.dam.2006.11.022}, url = {http://dx.doi.org/10.1016/j.dam.2006.11.022}, researchr = {https://researchr.org/publication/Tamm08-0}, cites = {0}, citedby = {0}, journal = {Discrete Applied Mathematics}, volume = {156}, number = {9}, pages = {1560-1566}, }