[news.eclipse.modeling.m2m] How to work with circular references?

[max.bureck@xxxxxxxxxxxxxxx (Max Bureck)]

Hello,

I'm having some trouble with circular references lately. How do I cope 
with the situation, that two output elements have references to the same 
third element?
In one case it was like that:

Input model:
A
|-B
|-B

Mappings:
A to X
B to Y,Z

Output model:
X
|-Y--Z
|-Y-/

So that both Y-model elements have a reference to the same Z.
Is there declarative way to express that?
My only idea is to create a helper-method, which is called in Mapping B to 
Y that checks if Z already exists. If Z exists, it returns it, if not, it 
calls a lazy rule creating Z. Is this the way to go, or is there a better 
way?