Many surfers are sitting on their surfboards in the calm ocean.
A group of surfers is surfing
Sitting does not imply surfing.
exists e1 s1 x1 x2 x3.(n_ocean(x3) & a_calm(s1) & Theme(s1,x3) & in(e1,x3) & on(e1,x2) & n_surfboard(x2) & of(x2,x1) & n_thing(x1) & Actor(e1,x1) & v_sit(e1) & n_surfer(x1) & n_quantity(x1))
exists e1 x1 x2.(Actor(e1,x1) & v_surf(e1) & of(x1,x2) & n_surfer(x2) & n_group(x1))