Abstract: 
In 1927, Lehmer presented criterions for primality, based on the converse of Fermat's litte theorem. This work formalizes the second criterion from Lehmer's paper, a necessary and sufficient condition for primality.
As a side product we formalize some properties of Euler's phifunction,
the notion of the order of an element of a group, and the cyclicity of the multiplicative group of a finite field. 
BibTeX: 
@article{LehmerAFP,
author = {Simon Wimmer and Lars Noschinski},
title = {Lehmer's Theorem},
journal = {Archive of Formal Proofs},
month = jul,
year = 2013,
note = {\url{http://isaafp.org/entries/Lehmer.html},
Formal proof development},
ISSN = {2150914x},
}
