%0 Journal Article %T %D 1990 %R 10.12386/A1990sxxb0033 %J Acta Mathematica Sinica, Chinese Series %P 288-288 %V 33 %N 2 %X %U https://actamath.cjoe.ac.cn/Jwk_sxxb_cn/EN/10.12386/A1990sxxb0033