冷(2)0 ne to one:ifa≠b, thenf。g(a)?≠f。g(b) &3)fand g are one-to-one correspondence, → fand g are onto.By(1),→f° g are onto By(2),→f° g are also one to one. Thus g is also one-to-one correspondence❖ (2)one to one:if ab，then f  g(a)? f  g(b) ❖ (3)f and g are one-to-one correspondence, f and g are onto. By (1), f  g are onto. ❖ By (2),  f  g are also one to one. Thus f  g is also one-to-one correspondence