Three people riding their bikes on a sidewalk.
The people are skateboarding down the sidewalk.
Three people can't be skateboarding when on their ride.
exists e1 x1 x2 x3 x4.(a_topic(x1) & on(e1,x4) & n_sidewalk(x4) & Theme(e1,x3) & Actor(e1,x2) & v_ride(e1) & n_bike(x3) & of(x3,x1) & n_thing(x1) & (x1 = x2) & n_people(x1) & card_eq_3(x1))
exists e1 x1 x2.(n_sidewalk(x2) & n_people(x1) & down(e1,x2) & Actor(e1,x1) & v_skateboard(e1))