Remember this argument

For a given n, a function

{0,1}ⁿ {0,1}

has  rows (input combinations).

A single function  can thus be characterized by a tuple of  0's and 1's.

Since there are such tuples, there are functions {0,1}ⁿ {0,1}

There are functions {0,1}ⁿ {0,1}