Some people are walking down the sidewalk in a city.
Some people are skateboarding down the sidewalk in a city.
Walking and skateboarding are not the same activity.
exists e1 x1 x2 x3.(n_sidewalk(x2) & down(e1,x2) & in(x2,x3) & n_city(x3) & Actor(e1,x1) & v_walk(e1) & n_people(x1))
exists e1 x1 x2 x3.(n_sidewalk(x2) & down(e1,x2) & in(x2,x3) & n_city(x3) & Actor(e1,x1) & v_skateboard(e1) & n_people(x1))