Weil, André (1958). 〈Final report on contract AF 18(603)-57〉. 《Scientific works. Collected papers》 (프랑스어) II. Berlin, New York: Springer-Verlag. 390–395, 545–547쪽. ISBN978-0-387-90330-9. MR537935.
arxiv.org
Basu, Samik; Basu, Somnath (2015). “Homotopy groups and periodic geodesics of closed 4-manifolds”. 《International Journal of Mathematics》 (영어) 26 (8): 1550059. arXiv:1303.3328. doi:10.1142/S0129167X15500597.