Create a process that is the sum of relationships of others processes

Hi,



    I want to create a process that is the sum of relationships of others processes.

    For example: I have the "P1" and "P2" processes. I want create a "P3" process that is the sum of "P1" and  "P2".

    

        

    If I use the "consolidation" function to sum the relationships of "P1" and "P2" I reach with "P3" with the sum of the relationships of "P1" and "P2", but I lose the relationships of "P1" and "P2".

    

    There is another way to sum "P1" and "P2" to "P3" without lose the relationships on "P1" and "P2"?

Thanks

Francisco