A snowboarder leaves a trail of snow on the mountain.
A snowboarder is skiing.
A snowboarder does not have to be on a mountain to be skiing.
exists e1 x1 x2 x3 x4.(n_mountain(x4) & Theme(e1,x2) & Actor(e1,x1) & v_leave(e1) & on(x2,x4) & of(x2,x3) & n_snow(x3) & n_trail(x2) & n_snowboarder(x1))
exists p1 x1.(exists x2.((x1 = x2) & n_skiing(x2)) & n_snowboarder(x1))