(def groups [[:rus :uru]
             [:spa :por :ira]
             [:fra :den]
             [:cro :nig :arg]
             [:bra :swi :ser]
             [:mex :ger :swe]
             [:eng :bel]
             [:jap :sen :col]])

(defn cross [[g1 g2]]
  (for [x g1 y g2] [x y]))

(defn possible-matchups [groups]
  (->> groups
       (partition 2)
       (mapcat cross)))

(doseq [matchup (possible-matchups groups)]
  (prn matchup))