Having a one-to-one correspondence between two things, where each element in one set matches exactly one element in another set.
From Latin 'bi-' (two) + 'univocal' (having one meaning or corresponding exactly). Univocal comes from 'unus' (one) + 'vox' (voice/meaning). The term evolved in mathematics to describe bijective relationships.
This word is essential in mathematics and logic—it's how we prove two infinite sets are the same size! For example, mathematicians use biunivocal correspondence to show that there are exactly as many even numbers as there are all natural numbers, which seems impossible but is totally true.
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