The article provides counting derangements of finite sets and counting non bijective functions. We provide a recursive formula for the number of derangements of a finite set, together with an explicit formula involving the number e. We count the number of non-one-to-one functions between to finite sets and perform a computation to give explicitely a formalization of the birthday problem. The article is an extension of [10].
@article{bwmeta1.element.doi-10_2478_v10037-010-0023-9, author = {Cezary Kaliszyk}, title = {Counting Derangements, Non Bijective Functions and the Birthday Problem}, journal = {Formalized Mathematics}, volume = {18}, year = {2010}, pages = {197-200}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.doi-10_2478_v10037-010-0023-9} }
Cezary Kaliszyk. Counting Derangements, Non Bijective Functions and the Birthday Problem. Formalized Mathematics, Tome 18 (2010) pp. 197-200. http://gdmltest.u-ga.fr/item/bwmeta1.element.doi-10_2478_v10037-010-0023-9/
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