JUBA, Feb. 2 (Xinhua) -- The United Nations Mission in South Sudan (UNMISS) on Sunday expressed concern about the escalating violence between cattle keepers and settled farming communities in Eastern ...
TIANJIN, Feb. 2 (Xinhua) -- In a studio adorned with antique charm in north China's Tianjin Municipality, Zhang Yu delicately rotated the clay sculpture with his left hand while skillfully carving ...
先熟悉一个数学概念,叫做置换(Permutation),在组合数学的领域也常被称作排列 我们知道,一个集合 A 到它自身的映射 A\rightarrow A 叫做变换(Transform) 如果这个集合 A 本身是有限集合,而且这个变换是个一一变换,此时这个变换就叫做置换 一个 n 元有限集合,能与集合 \left\{ 1,2,\cdots,n ...
Aviva Siegel, the wife of Israeli-American hostage Keith Siegel and herself a former captive, was excited as she left home to meet her husband as he was being handed over by Hamas on Saturday (Februar ...