Question 1173564
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If an element x belongs to the left hand side, then it belongs to one of the sets A, B or C.

Hence, it belongs to the set in the right hand side.



In opposite, if an element y belongs to the right hand side, then it belongs to one of the set A, B or C.

Hence, it belongs to the set in the left hand side.



It proves that the left hand side set is the same as the right hand side set,
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and the statement is proved.