题目内容
x2-{x2-[x2-(x2-1)-1]-1}-1.
x2-{x2-[x2-(x2-1)-1]-1}-1
=x2-{x2-[x2-x2+1-1]-1}-1
=x2-{x2-x2+x2-1+1-1}-1
=x2-x2+x2-x2+1-1+1-1
=0.
=x2-{x2-[x2-x2+1-1]-1}-1
=x2-{x2-x2+x2-1+1-1}-1
=x2-x2+x2-x2+1-1+1-1
=0.
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