a skateboarder grinds the rail.
The skateboarder has been grinding rails all morning.
Grinding the rail does not imply he has been doing it all morning.
exists e1 x1 x2.(n_rail(x2) & Theme(e1,x2) & Actor(e1,x1) & v_grind(e1) & n_skateboarder(x1))
exists x2.(n_skateboarder(x2) & all x1.(n_morning(x1) -> exists e1 x3.(Time(e1,x1) & Theme(e1,x3) & Actor(e1,x2) & v_grind(e1) & n_rail(x3))))