DEFINITIONG 函数 A function f whose domain and codomain are subsets of the set of real numbers is called strictly increasing if f(x)<f(y) whenever x <y and x and y are in the domain of f. Similarly, f is called strictly decreasing if f(x)>f(y) whenever x < y and x and y are in the domain of f
F u n c t i o n s 函 数 DEFINITION 6. A function f whose domain and codomain are subsets of the set of real numbers is called strictly increasing if f(x) < f(y) whenever x < y and x and y are in the domain of f. Similarly, f is called strictly decreasing if f (x) > f (y) whenever x < y and x and y are in the domain of f
DEFNNITION7。 函数 A function f from A to B is called onto, or surjective, if and only if for every element b EB there is an element a EA with f(a)=b A function f is called a surjection if it is onto 映上的,满函数,满射
F u n c t i o n s 函 数 DEFINITION 7. A function f from A to B is called onto, or surjective, if and only if for every element b∈B there is an element a∈A with f (a) = b. A function f is called a surjection if it is onto. 映上的，满函数，满射