A windsurfer surfs on frothy waves.
A person is practicing how to surf.
Surfs does not necessarily mean practicing how to surf.
exists e1 s1 x1 x2.(on(e1,x2) & n_wave(x2) & a_frothy(s1) & Theme(s1,x2) & Actor(e1,x1) & v_surf(e1) & n_windsurfer(x1))
exists e1 x1 x2.(Topic(e1,x2) & Actor(e1,x1) & v_practice(e1) & n_manner(x2) & exists e2 x3.(Actor(e2,x3) & v_surf(e2)) & n_person(x1))