Cezary Kaliszyk. Counting Derangements, Non Bijective Functions and the Birthday Problem. Formalized Mathematics, 18(1-4):197-200, 2010. [doi]
@article{Kaliszyk10,
title = {Counting Derangements, Non Bijective Functions and the Birthday Problem},
author = {Cezary Kaliszyk},
year = {2010},
doi = {10.2478/v10037-010-0023-9},
url = {http://dx.doi.org/10.2478/v10037-010-0023-9},
researchr = {https://researchr.org/publication/Kaliszyk10},
cites = {0},
citedby = {0},
journal = {Formalized Mathematics},
volume = {18},
number = {1-4},
pages = {197-200},
}