The boy is cutting the grass.
The boy cut the grass.
Cut the grass implies the act of cutting the grass is complete.
exists e1 x1 x2.(n_grass(x2) & n_boy(x1) & Theme(e1,x2) & Actor(e1,x1) & v_cut(e1))
exists e1 x1 x2.(n_grass(x2) & n_boy(x1) & Theme(e1,x2) & Actor(e1,x1) & v_cut(e1))