php4 classes, extending same class

I have the following classes being inherited: User extends School I have two classes: Profile extends User and Buddies extends User being used in the same .php file. I get a "Fatal error: Cannot redeclare class school in ..." I can see why this is happening but three questions, 1. Does php5 allow for multiple extends? e.g. Profile extends User extends School 2. Programmatically, how can I resolve this sort of issue besides not using this class and making a new class with a different name? 3. Is there a way to uninclude a included file? Thanks in advance.