Bike riders are racing each other.
Bike riders race.
In order to race you need another person. If a bike rider is racing it means that they are racing each other.
exists x1 x2.(all x3.(n_other(x3) -> exists e1.(Theme(e1,x3) & Actor(e1,x1) & v_race(e1))) & n_rider(x1) & (x1 = x2) & ne_nam_bike(x2))
exists s1 x1 x2 x3.(n_race(x1) & a_.(s1) & Theme(s1,x1) & of(x1,x3) & n_rider(x3) & (x1 = x2) & ne_nam_bike(x2) & a_topic(x1))