@book{nathanson1996,
  title={Additive Number Theory: The Classical Bases},
  author={Nathanson, Melvyn Bernard},
  series={Graduate Texts in Mathematics},
  volume={164},
  year={1996},
  publisher={Springer},
  address={New York}
}
@article{Three_Squares-AFP,
  author  = {Anton Danilkin and Loïc Chevalier},
  title   = {Three Squares Theorem},
  journal = {Archive of Formal Proofs},
  month   = {May},
  year    = {2023},
  note    = {\url{https://isa-afp.org/entries/Three_Squares.html},
            Formal proof development},
  ISSN    = {2150-914x},
}