In mathematics, a function that pairs each element from one set with exactly one unique element from another set, with no elements left unpaired.
From bi- (two) combined with injection (from Latin iacere, to throw), coined in mid-20th-century mathematics to describe one-to-one and onto functions.
Bijections are the mathematical way of saying 'I can pair these two groups perfectly with nothing left over'—which is why they're crucial for proving that different infinities are actually the same size!
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