BibTeX: 
@article{Falling_Factorial_SumAFP,
author = {Lukas Bulwahn},
title = {The Falling Factorial of a Sum},
journal = {Archive of Formal Proofs},
month = dec,
year = 2017,
note = {\url{http://isaafp.org/entries/Falling_Factorial_Sum.html},
Formal proof development},
ISSN = {2150914x},
}
