in rivals of

[Gość: lelum]

seems an expression to something like "opposed by"

[Gość: Steve]

It is used as "among competitors of" eg a drug contains 30% active content; in
rivals of this drug there is only 20%; you can find better facilities in rivals
of the Sheraton. There are references to films/programmes eg there is
information about Christian secrets in Rivals of Jesus, produced by National
Geographic.