BibTeX: 
@article{Card_PartitionsAFP,
author = {Lukas Bulwahn},
title = {Cardinality of Set Partitions},
journal = {Archive of Formal Proofs},
month = dec,
year = 2015,
note = {\url{https://isaafp.org/entries/Card_Partitions.html},
Formal proof development},
ISSN = {2150914x},
}
