摘要Let G be an arbitrary group with identity e. Let A be a G-graded ring with identity 1, i. e. A= A<sub>g</sub> （direct sums of additive groups）, with property A<sub>g</sub>A<sub>h</sub> A<sub>gh</sub>. The smash prod-
3YIN Yanmin School of Mathematical Sciences, Peking University, Beijing 100871, China,Department of Mathematics, Shandong Institute of Architecture and Engineering, Jinan 250101, China.Morita contexts on the Hopf algebroid[J].Science China Mathematics,2005,48(7):958-971.
9FAN Yun & ZHU Ping School of Mathematics and Statistics, Central China Normal University, Wuhan 430079, China School of Mathematical Science, Nankai University, Tianjin 300071, China.A theorem of Fong's type for graded algebras[J].Science China Mathematics,2005,48(5):577-582.
