The problem is that for every finite description of f, the x that fulfills f(x)=5 is not in the set of numbers than cannot be described by a finite set of symbo

The problem is that for every finite description of f, the x that fulfills f(x)=5 is not in the set of numbers than cannot be described by a finite set of symbols. (I assume here that there is only one solution of f(x)=5)