Injective function
From Citizendium, the Citizens' Compendium
In mathematics, an injective function or one-to-one function or injection is a function which has different output values on different input values: f is injective if 
implies that 
.
An injective function f has a well-defined partial inverse 
. If y is an element of the image set of f, then there is at least one input x such that 
. If f is injective then this x is unique and we can define 
to be this unique value. We have 
for all x in the domain.
A strictly monotonic function is injective, since in this case 
implies that 
.
