@article{oai:soar-ir.repo.nii.ac.jp:00018403,
 author = {Futa, Yuichi and Okazaki, Hiroyuki and Shidama, Yasunari},
 issue = {4},
 journal = {Formalized Mathematics},
 month = {Dec},
 note = {Article, Formalized Mathematics. 20(4): 257-280 (2012)},
 pages = {257--280},
 title = {Free Z-module},
 volume = {20},
 year = {2012}
}