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. 函數兩組元素一一對應的規則,第一組中的每個元素在第二組中只有唯一的對應量
Don't forget to take a change of (ie a second set of) clothes. 不要忘記帶著替換的衣服。