Heath-Brown, Roger Max Planck Institute for Mathematics, Max Planck Society;
https://doi.org/10.1515/crll.2003.037 (Publisher version)
Heath-Brown, R., & Tolev, D. I. (2003). Lagrange's four squares theorem with one prime and three almost-prime variables. Journal für die Reine und Angewandte Mathematik, 558, 159-224. doi:10.1515/crll.2003.037.