DEFINITIONS 函数 A function f is said to be one-to-one, or injective, if and only f(x)=f(y) implies that x=y for all x and y in the domain of. A function is said to be an injection if it is one-to-one 对一,单函数,单射F u n c t i o n s 函 数 DEFINITION 5. A function f is said to be one-to-one, or injective, if and only f (x) = f (y) implies that x = y for all x and y in the domain of f. A function is said to be an injection if it is one-to-one. 一对一，单函数，单射