People are river rafting.
People are rafting in the ocean
Not all river rafting are rafting in the ocean.
exists e1 x1 x2.(Time(e1,x2) & n_river(x2) & Actor(e1,x1) & v_raft(e1) & n_people(x1))
exists e1 x1 x2.(n_ocean(x2) & in(e1,x2) & Actor(e1,x1) & v_raft(e1) & n_people(x1))