Theorem 3.2: Let f be a(everywhere) function from a to B, andAcA(i-1, 2,,n). Then (1)f(4)=Uf(4) (2)f(4)∩f(4) i=1❖ Theorem 3.2：Let f be a (everywhere) function from A to B, and AiA(i=1,2,…n). Then   n i i n i f Ai f A 1 1 (1) ( ) ( ) = = =   n i i n i f Ai f A 1 1 (2) ( ) ( ) = = 