Defining measure It should be a nonegative set function Le, u: X->R+ Lots of functions likes these not all can be called measure:制定规则 ·规则1:空集的测度为0 规则2任意多个互不相交集合的总测度等于各子 测度之和( countable additivity) 这等于什么都没说, but check it before adding more rulesDefining Measure • It should be a nonegative set function – i.e., u: X->R+ • Lots of functions likes these, not all can be called measure: 制定规则 • 规则1: 空集的测度为0 • 规则2: 任意多个互不相交集合的总测度等于各子 测度之和 （countable additivity） • 这等于什么都没说，but check it before adding more rules!