Identity function
An identity function f is a function which doesn't have any effect: it always returns the same value that was used as its argument.Formally, if M is a set, we define the identity function idM on M to be that function with domain and codomain M which satisfies
- idM(x) = x for all elements x in M.
When choosing M equal to the positive integers, one obtains the identity function Id(n), which is a multiplicative function considered in number theory.
