A young boy is sitting on the grass.
The grass is actually molten lava.
A boy could not be sitting on the grass if the grass is actually molten lava.
exists e1 s1 x1 x2.(n_grass(x2) & on(e1,x2) & Actor(e1,x1) & v_sit(e1) & n_boy(x1) & a_young(s1) & Theme(s1,x1))
exists s1 s2 x1 x2.(n_grass(x1) & a_actually(s2) & Manner(s1,s2) & Time(s1,x2) & n_lava(x2) & Theme(s1,x1) & a_molten(s1))