[Exim] relay to first MX only

hi,

finaly, i am using a perl script to relay only to the primary MX,
Nico Erfurth config was very nice, thank, but more to play with
(I gave me the idea of creating a turing machine only with exim router config,
for a joke)
about my question for check_ancestor and repeat_use,
can someone explain me what those option does, because if i have corectly read
the doc, it is possible to use them to drop loop checkeking, but it still
prevent looping (yes i need looping !)

thank

Edouard