<p>The sum <math>x + x\!</math> generally denotes no logical term. But <math>x,_\infty + \, x,_\infty</math> may be considered as denoting some two <math>x\!</math>'s.</p>
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<p>The sum 'x' + 'x' generally denotes no logical term. But 'x',<sub>∞</sub> + 'x',<sub>∞</sub> may be considered as denoting some two 'x's.</p>
<p>It is natural to write:</p>
<p>It is natural to write:</p>
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: <p>'x' + 'x' = !2!.'x'</p>
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{| width="100%"
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| width="10%" |
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<p>and</p>
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| align="center" | <math>x + x ~=~ \mathit{2}.x</math>