A man surfing.
A man is surfing.
" A man is surfing " is a rephrasing of " A man surfing "
exists x1 x2.(a_topic(x1) & n_surfing(x1) & of(x1,x2) & n_man(x2))
exists e1 x1.(Actor(e1,x1) & v_surf(e1) & n_man(x1))