Example: Let A=1, 233, 49,B-a,b, cl R1=(1,a)(2,b),(3,c)}, R2={(1,a)2(1,b)(2,b),(3,c)2(4,c)}, R3={(1,a),(2b),(3,b)4,a)} Example: LetA=(-2, -1, 0, 1, 2) and B={0,1,2,3,4,5}. 令Let广={(-2,0),(-1,1),(0,0),(1,3),(2,5)}.fisa (everywhere)function 今X={-2,0,1},f(X)= Y={0,5},f1(Y)=?❖Example：Let A={1,2,3,4},B={a,b,c}, ❖R1={(1,a),(2,b),(3,c)}, ❖R2={(1,a),(1,b),(2,b),(3,c),(4,c)}, ❖R3={(1,a),(2,b),(3,b),(4,a)} ❖Example: Let A ={-2,-1, 0,1,2} and B={0,1,2,3,4,5}. ❖ Let f={(-2,0),(-1,1), (0,0),(1,3),(2,5)}. f is a (everywhere)function. ❖ X={-2,0,1}, f(X)=? ❖ Y={0,5}, f -1 (Y)=?