Three speed skaters skating.
Some people are skating.
Three speed skaters are collectively called as people.
exists e1 x1 x2.(Actor(e1,x1) & v_skate(e1) & n_skater(x1) & of(x1,x2) & n_speed(x2) & card_eq_3(x1))
exists e1 x1.(Actor(e1,x1) & v_skate(e1) & n_people(x1))