若f是非空集合A到非空集合B的一个单值对应,即对任意a∈A,按照对应法则f,有唯一的b∈B与之对应,则称这个对应f为A到B的一个映射,记作b=f(a),又记f(A)={f(a)|a∈A},则一般有f(A)(?)B。特别地,若f(A)=B,则称映射为满射。若f(A)=B,且当a_1≠a_2时,有f(a_1)≠f(a_2)那么称映射f为A到B的一一映射。这时f有一个逆映射f~(-1),满足对任意a∈A,有f~(-1)(f(a))=a,对任意b∈B有f(f~(-1)(b))=b。 If f is a non-empty set A to a non-empty set B corresponding to a single value, that is, for any a ∈ A, in accordance with the corresponding law f, there is a unique b ∈ B corresponds to it, then said the corresponding f is A to A () () (), () () () () () () In particular, if f (A) = B, the mapping is said to be full shot. If f (A) = B, and when a_1 ≠ a_2, then f (a_1) ≠ f (a_2) then the mapping f is the one-to-B mapping. In this case f has an inverse mapping f ~ (-1), satisfying f (-1) (f (a)) = a for any a∈A and f (f ~ (-1) for any b∈B ) (b)) = b.