>>12282007You can just do it exhaustively. Like all the permutations of these options:
a = approaching 1 or approaching infinity
b = approaching 0 or approaching 1
c = approaching 1 or approaching infinity
d = approaching 0 or approaching 1
That's 16 trends to look at. Just show that none of these extremes get to 1, and that'll prove that nothing in between those extremes will get to 1.
