DFDs

Hi, i am expanding on an existing software system developed earlier by some people who have left. Their software design was done in the form of Data Flow Diagrams.

I added a new module Z where one of the 3 functions of Z is to be called from the central module (A) of the original system.

I have portrayed Z as another DFD on the same level as A. What troubles me is that A can call either of the 3 functions in Z, how can i portray this using the DFD structure i had just mentioned?

An example of this situation is a core module calling any of the mathematical functions within another module.

Pls advice