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=a²-b²-2(a²-b²)+a²+b²=
=a²-b²-2a²-2b²+a²+b²=
=-2b²
=a²-2ab+b²-2(a²-b²)+a²+2ab+b²=
=a²-2ab+b²-2a²-2b²+a²+2ab+b²=
=0