Why is f not a function from R to R if

a) f(x)=1x?

f(x) is not well-defined because there are two distinct values assigned to each x.
f(0) is not defined.
f(x) is not defined for x

Question

Why is f not a function from R to R if
 
a) f(x)=1x?
 
 
		f(x) is not well-defined because there are two distinct values assigned to each x.
		f(0) is not defined.
		f(x) is not defined for x<0.

solomonzelman · Answer

Is it  $\large\color{black}{   f(x)=1\times x   }$  which is same as  $\large\color{black}{   f(x)=x   }$
OR, is it supposed to be,  $\large\color{blue}{   f(x)=1^x   }$   ?