cycles in dependency structure

Hello Friends
Can somebody explain the following from Martin Fowler page 112, last 2 lines.

Putting abstract classes in supertype package is good way of breaking cycles in the dependency structure

what are these cycles being referred ?
Thanks
Ram Kondawar
[This message has been edited by Ram Kondawar (edited June 12, 2001).]
[This message has been edited by Ram Kondawar (edited June 12, 2001).]
[This message has been edited by Ram Kondawar (edited June 12, 2001).]

I am sorry for the font size, it was a typo error

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Thank you Johannes . I did edit the message.
Ram Kondawar

Hi,
This is based on Indirection Pattern.
By keeping supertype abstract, the class which sends the message to the supertype doesn't know about the type of object (subtype) it is refering to until runtime.Since, the sender class is not directly coupled with the subtype, the temporary visibility (local or parameter) of the subtype is broken by indirection.
Since dependency relates to above types of visibility,we have reduced the dependency cycles between classes by allowing the abstract supertype to talk to its subtype.
Hope this helps,
Sandeep
[This message has been edited by Desai Sandeep (edited June 12, 2001).]

Thanks Sandeep
This has definitely cleared my doubt.Till I had read your message , I was wondering how the dependency of subtype on supertype reduces by putting abstract supertype in separate package.
Thanks
Ram