A boy sand surfing down a hill
The girl surfed the waves.
One cannot be a girl and boy at once and one cannot sand surf on the water, and one cannot surf on land.
exists e1 s1 x1 x2 x3 x4.(a_topic(x1) & a_down(s1) & Manner(e1,s1) & Theme(e1,x4) & Actor(e1,x3) & v_surf(e1) & n_hill(x4) & (x1 = x3) & n_sand(x1) & of(x1,x2) & n_boy(x2))
exists e1 x1 x2.(n_wave(x2) & n_girl(x1) & Theme(e1,x2) & Actor(e1,x1) & v_surf(e1))