Burghelea, Dan Max Planck Institute for Mathematics, Max Planck Society;
https://doi.org/10.1007/s00454-013-9497-x (Publisher version)
Burghelea, D., & Dey, T. K. (2013). Topological persistence for circle valued maps. Discrete & Computational Geometry, 50(1), 69-98. doi:10.1007/s00454-013-9497-x.