A guy mowing a lawn on his tractor
A guy riding on a snowmobile.
A guy can not be mowing a lawn on his tractor while riding on a snowmobile.
exists e1 x1 x2 x3 x4.(a_topic(x1) & Theme(e1,x3) & Actor(e1,x2) & v_mow(e1) & on(x3,x4) & n_tractor(x4) & of(x4,x1) & n_male(x1) & n_lawn(x3) & (x1 = x2) & n_guy(x1))
exists x1 x2 x3.(a_topic(x1) & on(x1,x3) & n_snowmobile(x3) & Time(x1,x2) & n_riding(x2) & n_guy(x1))