维基百科:In the 1960s, it was proved that Kirkman triple systems exist for all orders n = 3 (mod 6). This was first proved by Lu Jiaxi (Chinese: 陆家羲) in 1965, but was not published at that time. In 1968, it was proven independently by D. K. Ray-Chaudhuri and R. M. Wilson.
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2021年10月25日,海关总署发布2021年第84号公告,自2021年12月1日起,海关不再对输欧盟成员国、英国、加拿大、土耳其、乌克兰和列支敦士登等国家货物签发普惠制(Generalized System of Preferences 普遍优惠制度,简称 普惠制 GSP)原产地证书。 customs.gov.cn/customs/302249…
普遍优惠制度(Generalized System of Preferences)是发达国家(给惠国)对发展中国家及地区(受惠国)出口制成品和半制成品给予普遍的、非歧视的、非互惠的关税优惠制度。
自1978年以来,世界上先后有40个国家给予中国普惠制关税优惠,分别为:欧盟27国、英国、欧亚经济联盟3国(俄罗斯、白俄罗斯、