we know that a bijective function is both injective and surjective(adsbygoogle = window.adsbygoogle || []).push({});

injective means that unique values in the domain map to unique values in the codomain

surjective means that all of the values in the codomain are mapped.

but then, what of values in the domain that cannot be mapped to the codomain? (maybe we could take, for example, values of x < 0 for the function ln(x)).

for example

http://en.wikipedia.org/wiki/Image:Injection.svg

now, is Y -> X injective and surjective? Unique values within Y map to unique values within X, and all values of X are covered, if we count X as the codomain...

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# Question about injectivity/surjectivity => bijectivity

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