A dirt biker with number 625 is racing on a course.
a dirt bike racer on course who is in the lead
A dirt biker with number 625 is racing on a course does not mean he is on course who is in the lead
exists e1 x1 x2 x3 x4.(on(e1,x4) & n_course(x4) & Actor(e1,x1) & v_race(e1) & with(x1,x3) & n_number(x3) & card_eq_625(x3) & n_biker(x1) & of(x1,x2) & n_dirt(x2))
exists p1 x1 x2 x3 x4 x5 x6.(n_lead(x6) & a_topic(x1) & on(x1,x4) & in(x5,x6) & (x4 = x5) & n_course(x4) & n_racer(x1) & of(x1,x3) & n_bike(x3) & of(x1,x2) & n_dirt(x2))