Apple Logic Pro /LogicExpress Discussion

Ok, I should know the answer to this but I don't: As I look in my files, under the name of some project entitled, say "Friends", there are a whole collection of files with the following titles:  friends.00.lso, friends.01.lso, friends.02.lso, friends.03.lso, etc. (for Logic 7) and/or  friends.00.logic, friends.01.logic, friends.02.logic, friends.03.logic, etc. (for Logic 8).   

How do these files come to be?  Is it something that I somehow cause?  Furthermore, I don't know which version is my latest --- although I usually go to the highest number.  

What should I know about this?

Thanks for your patience.


Tim

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