This should've been an easy problem for me, though a few small details make it tougher than I'd initially thought.
Let be defined as follows: (this is the main part that has me stumped right now)
for all unless ,
for all where .
Show that as on any straight line through .
Determine if exist as .
If I were to get past that little hurdle in terms of the definition of , I could probably get through the rest using epsilon-delta proofs.