There is this problem in my book says:
"Ptah is an Egyptian God, and he is the father of all Egyptian gods. Therefore, he is the father of himself."
I see the premises as something like this: $$\forall x[Gx \Rightarrow Fyx]$$ $$Gp$$
So, I try to do the following using universal specification: $$Gp \Rightarrow Fpp$$
I just substitute $p$ for Ptah to both $x$ and $y$. But is it the right thing to do? And by using modus ponen, can we say that it is valid that Ptah is the father of himself??