o Theorem 3.10: Let be one-to-one correspondence between A and B, andf be one-to-one correspondence between B and c Then ()-=gl of-I o Proof: By Theorem 3.6,f og is one-to-one correspondence from A to C o Similarly, By theorem 3.7, 3.8, 8- is a one-to one correspondence function from B to A, and f-l is a one-to-one correspondence function firom c to B❖ Theorem 3.10：Let g be one-to-one correspondence between A and B, and f be one-to-one correspondence between B and C. Then (fg) -1= g -1 f -1 ❖ Proof: By Theorem 3.6, f g is one-to-one correspondence from A to C ❖ Similarly, By theorem 3.7, 3.8, g -1 is a one-to￾one correspondence function from B to A, and f –1 is a one-to-one correspondence function from C to B