gcc and shared library

[D Jemms]

Greetings,
I am relatively new to Linux world and I need some 
information of Shared Libraries under Linux.
I have one program say test.c and a shared library
libfoo.so 
Questions are:
1. can I have extern variables in shared library?
2. can I have two shared libraries linked to a same
executable and function abc() has it's body in both
the shared libraries.Is this possible ?

Help on this will be highly appreciated.

-DJ

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