Question 1039163
<pre>
In general,
A function graph must not pass above or below itself.
Therefore, for its inverse to be a function, it must not 
pass either to the right or left of itself. 

Or ---

A function graph must pass the vertical line test.  That is,
no vertical line can intersect the graph more than once.  
Therefore, in order for a function to have an inverse which 
is also a function, its graph must pass the horizontal line 
test.  That is, no horizontal line can intersect the graph 
more than once.

Edwin</pre>