If I make a vow to not eat pizza, what can I not eat?
On the one hand, it would seem that bread with sauce and cheese on it is called pizza, as that is what they give you in a pizza shop when you order a slice of pizza.
However, it is implied otherwise in the bagel-bites commercial song:
Pizza in the morning pizza in the evening pizza at suppertime/
When pizza's on a bagel you can eat pizza anytime
It is clear that the pizza is on the bagel. This would lead me to believe that the real pizza is the tomato-based-sauce and the melted cheese, and the bread is just the base to put it on.
However, one would expect according to this that spaghetti with cheese and sauce would also be a form of pizza and called thus, since it contains a melted-cheese/tomato-bases-sauce mixture, which is something we don't see. And if the requirement is that the cheese-sauce mixture is a layer on top, I present lasagna, which is also not known as pizza.
So if I make a vow to not eat pizza, what can I not eat? Please cite your sources.