I bought a 2009 Macbook Pro 13" used from someone and it doesn't have the install disc for Snow Leopard which is currently installed. If I have to restore the computer someday can I use a friends Snow Leopard Install Disc?

I'm not sure how the licensing works. All I know is right now I have a legit version of Snow Leopard on the computer. The install disc's are like $50 and I don't want to buy one unless I have to.