BibTeX: 
@article{Arith_Prog_Rel_PrimesAFP,
author = {José Manuel Rodríguez Caballero},
title = {Arithmetic progressions and relative primes},
journal = {Archive of Formal Proofs},
month = feb,
year = 2020,
note = {\url{https://isaafp.org/entries/Arith_Prog_Rel_Primes.html},
Formal proof development},
ISSN = {2150914x},
}
