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**r7iris** Let X be a set and let A be one of its subsets. The characteristic function of A is the function Q_A: X--> {0,1} defined by

Q_A (x)= {1 if x is in A,

{0 if x is not in A.

a) show that if A and B are subsets of X then they have the same characteristic function iff they are equal.

b) Show that every function from X to {0,1} is the characteristic function of some subset of X.

Actually, I dont know understand what is the relationship between sets and characteristic functions...

Please help me or give me some hints.