BibTeX: 
@article{Robinson_ArithmeticAFP,
author = {Andrei Popescu and Dmitriy Traytel},
title = {Robinson Arithmetic},
journal = {Archive of Formal Proofs},
month = sep,
year = 2020,
note = {\url{http://isaafp.org/entries/Robinson_Arithmetic.html},
Formal proof development},
ISSN = {2150914x},
}
