Englishfor English speakers
reciprocity
Noun
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Reciprocity is a relationship in which a something is given, and something is expected back in return.
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Reciprocity is a relationship which means quid pro quo or "fair trade".
You scratch my back, and I'll scratch your back: that's reciprocity.
theorem
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noun
a proposition deducible from basic postulates
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noun
an idea accepted as a demonstrable truth