A injection is a function `f:X→Y`

such that
for each `y∈Y`

there is at most one `x∈X`

such that `f(x)=y`

.
Another way of stating this is that if `x≠y`

then `f(x)≠f(y)`

.

The function `f(x)=x`

is an injection.
The function `f(x)=x`

is not an injection.
^{2}

A. Menzes, P. van Oorschot, and S. Vanstone, *Handbook of Applied Cryptography.* CRC Press, 1996.

Copyright © 2014 Barry Watson. All rights reserved.