https://dds.las.ac.cn/service/document?appId=a1vacbnPuv9qJRzJvdNXfsesj9JbIa6e&appKey=sPBA4vANLzjnW1k5eufEcc4k7dxfNraW&ts=1763029733705&signature=da2a12fa38a531a5e42db3b4f6981d58&articleTitle=Papers+on+Group+Theory+and+Topology&articleAuthor=Max+Dehn&publicationTitle=Papers+on+Group+Theory+and+Topology&language=&publicationType=1&publishYear=1987&isn=9781461291077&publisher=Springer+New+York