a quick guess is that a), b) and d) are never possible and c) is always possible.
an irrational number should always exist:
If x=2 then y^y = 5 and y is a bit over 2
If x=3 then y^y = 36 and y is a bit over 3
the real question is whether any of these is rational. I don't think raising a rational noninteger to itself can yield an integer you might not even be able to make it rational.
for example (9/2)^(9/2) = 9^(9/2) / 2^(9/2) = 19683 / 16√2
as for part d) a complex to a complex power is not well defined, but I don't think it can give a real value if the base and power are the same. I may have to play around with this one.

Posted by Jer
on 20120122 02:00:19 