a boy walks through the lawn.
A man shoveling snow.
cannot be shoveling and walking at the same time.
exists e1 x1 x2.(n_lawn(x2) & through(e1,x2) & Actor(e1,x1) & v_walk(e1) & n_boy(x1))
exists e1 x1 x2 x3.(a_topic(x1) & Theme(e1,x3) & Actor(e1,x2) & v_shovel(e1) & n_snow(x3) & (x1 = x2) & n_man(x1))