期刊名称：International Journal of Mathematics and Mathematical Sciences
印刷版ISSN：0161-1712
电子版ISSN：1687-0425
出版年度：2005
卷号：2005
DOI：10.1155/IJMMS.2005.487
出版社：Hindawi Publishing Corporation
摘要：We prove the existence of a dense subset Δ of [0,4] such that for all α∈Δ there exists a subgroup Xα of infinite rank of ℤ[z] such that Xα is a discrete subgroup of C[0,β] for all β≥α but it is not a discrete subgroup of C[0,β] for any β∈(0,α).
