山东大学学报(理学版) ›› 2016, Vol. 51 ›› Issue (10): 22-27.doi: 10.6040/j.issn.1671.9352.0.2016.037
李焕云,乔虎生
摘要: 设S是幺半群, FGWI, WPF, STF分别表示有限生成弱内射右S系、弱拉回平坦右S系和强挠自由右S系的类。证明了在有左零元的左reversible幺半群上,每一个右S系Ai∈FGWI当且仅当∪[DD(-*3]·[DD)]i∈IAi∈FGWI;在Noetherian幺半群上,任意fg弱内射S系的有向上极限是fg弱内射的;同时考虑了WPF覆盖和STF覆盖,给出了每一个右S系都有FGWI覆盖的条件。证明了若S是有有限几何型的有限生成幺半群,每一个右S系都有WPF覆盖,以及在任意幺半群S上,每一个右S系都有STF覆盖。
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