TY - JOURNAL OF SHANDONG UNIVERSITY(NATURAL SCIENCE) A1 - LI Yuan, YAO Hai-lou T1 - On torsion free class and cover class in category of comodules Y1 - JF - JOURNAL OF SHANDONG UNIVERSITY(NATURAL SCIENCE) JO - JOURNAL OF SHANDONG UNIVERSITY(NATURAL SCIENCE) SP - 1 EP - 5 VL - 55 IS - 8 UR - http://lxbwk.njournal.sdu.edu.cn N1 - 10.6040/j.issn.1671-9352.0.2019.869 ER -