https://dds.las.ac.cn/service/document?appId=a1vacbnPuv9qJRzJvdNXfsesj9JbIa6e&appKey=sPBA4vANLzjnW1k5eufEcc4k7dxfNraW&ts=1763049778890&signature=9d9a4fe9fc002561568d43489f5edf60&articleTitle=Papers+on+Group+Theory+and+Topology&articleAuthor=Max+Dehn&publicationTitle=Papers+on+Group+Theory+and+Topology&language=&publicationType=1&publishYear=1987&isn=9780387964164&publisher=Springer+New+York