问题描述：
英语数学题翻译
Let X be a finite set of positive integers and A a subset of X. Prove that there exists a subset B of X such that A equals the set of elements of X which divide an odd number of elements of B.
Let X be a finite set of positive integers and A a subset of X. Prove that there exists a subset B of X such that A equals the set of elements of X which divide an odd number of elements of B.
问题解答：
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