@inbook{+2010+221+221,
url = {https://doi.org/10.1515/9781400830398.221b},
title = {III.39 Homotopy Groups},
booktitle = {The Princeton Companion to Mathematics},
editor = {Timothy Gowers and June Barrow-Green and Imre Leader},
publisher = {Princeton University Press},
address = {Princeton},
pages = {221--221},
doi = {doi:10.1515/9781400830398.221b},
isbn = {9781400830398},
year = {2010},
lastchecked = {2026-05-09}
}