A rule of correspondence between two sets such that there is a unique element in the second set assigned to each element in the first set 函数两组元素一一对应的规则，第一组中的每个元素在第二组中只有唯一的对应量
2.
A rule of correspondence between two sets such that there is a unique element in the second set assigned to each element in the first set 函数两组元素一一对应的规则，第一组中的每个元素在第二组中只有唯一的对应量。
3.
A rule of correspondence between two sets such that there is a unique element in the second set assigned to each element in the first set 应变量，函数一个与他量有关联的变量，这一量中的任何一值都能在他量中找到对应的固定值。
