Cycles

[orbitz]

I'm trying to implement a protocol and one of the aspects of the 
protocol is the ability to transmit cyclic data.  Erlang's nature seems 
to only allow tree-structures.  Is there anything I can do to handle this?
I could just error out on cycles and tell the client i can't accept this 
data, but it makes the protocol practically useless from there, and I'd 
rather not have the clients be forced to worry about "what if the server 
is implemented in erlang".

Any suggestion are appreciated, thank you.