https://dds.las.ac.cn/service/document?appId=a1vacbnPuv9qJRzJvdNXfsesj9JbIa6e&appKey=sPBA4vANLzjnW1k5eufEcc4k7dxfNraW&ts=1763013079394&signature=34c24e4d4e008bdc1f99314b6de41fec&articleTitle=Classical+Topology+and+Combinatorial+Group+Theory&articleAuthor=John+Stillwell&publicationTitle=Classical+Topology+and+Combinatorial+Group+Theory&language=&publicationType=1&publishYear=1980&isn=9781468401127&publisher=Springer+US