TY - JOURNAL OF SHANDONG UNIVERSITY(NATURAL SCIENCE) A1 - LIU Zu-hua, GUO Yu-qi T1 - The concatenation of thin languages and r-disjunctive languages ——several studies on combinatorial semigroups(Ⅰ) Y1 - JF - JOURNAL OF SHANDONG UNIVERSITY(NATURAL SCIENCE) JO - JOURNAL OF SHANDONG UNIVERSITY(NATURAL SCIENCE) SP - 2 EP - 7 VL - 54 IS - 6 UR - http://lxbwk.njournal.sdu.edu.cn N1 - 10.6040/j.issn.1671-9352.0.2019.172 ER -