Ira M. Gessel. Counting acyclic digraphs by sources and sinks. Discrete Mathematics, 160(1-3):253-258, 1996. [doi]
@article{Gessel96,
title = {Counting acyclic digraphs by sources and sinks},
author = {Ira M. Gessel},
year = {1996},
doi = {10.1016/0012-365X(95)00119-H},
url = {http://dx.doi.org/10.1016/0012-365X(95)00119-H},
tags = {source-to-source, open-source},
researchr = {https://researchr.org/publication/Gessel96},
cites = {0},
citedby = {0},
journal = {Discrete Mathematics},
volume = {160},
number = {1-3},
pages = {253-258},
}