  We investigate the effective case of two-flavor neutrino oscillations in
infinitely dense matter by using a perturbative approach. We begin by briefly
summarizing the conditions for the three-flavor neutrino oscillation
probabilities to take on the same form as the corresponding two-flavor
probabilities. Then, we proceed with the infinitely dense matter calculations.
Finally, we study the validity of the approximation of infinitely dense matter
when the effective matter potential is large, but not infinite, this is done by
using both analytic and numeric methods.
