Recursive structures...

[zet]

Hello!

I'm trying to run such a predicate:

rs:- _qbar=nand:X(a:in, b:out, c:_q),
     _q=nand:X(e:in, f:out, g:_qbar)    % just for example
     assertz(genl(_qbar)),
     assertz(genl(_q)).

It just kills gprolog interpreter, leaving core dump and message about
segfault.
Can somebody give me a hint on how to create such structures in GNU Prolog,
or how such   structures can be replaced with alternative...

Thanks in advance.