Plantiga's ontological argument.

[Shell B]

Let me rewrite it in symbol form. N = necessary, and p = possible, so Nx means 'its necessary that x' and px means that 'its possible that x'. Finally, > means 'if...then'.

a. px > Npx
b. not Npx > not px
c. not Npx > N not x
d. p not px > N not x
e. pN not x > N not x
f. pNx > Nx

Blurgh, that is sloppy. Let's use * for possible. # for necessary and ~ for not.

a. *x > #*x
b. ~ #*x > ~ *x
c. ~ #*x > # ~x
d. * ~ *x > # ~x
e. *# ~x > # ~x
f. *#x > #x

I'll try to scrape through that in the morning.

Chew on this for a moment, though. Even if your first premise here isn't flawed, this becomes a problem. http://en.wikipedia.org/wiki/Vacuous_truth