Baues, Hans-Joachim Max Planck Institute for Mathematics, Max Planck Society;
Muro, Fernando Max Planck Institute for Mathematics, Max Planck Society;
https://doi.org/10.1515/FORUM.2008.032 (Publisher version)
Baues, H.-J., & Muro, F. (2008). Secondary homotopy groups. Forum Mathematicum, 20(4), 631-677. doi:10.1515/FORUM.2008.032.