Someone is surfing underneath a wave on a white surfboard.
There is someone on a surfboard.
Someone surfing implies that someone is on a surfboard.
exists e1 s1 x1 x2 x3.(underneath(e1,x2) & on(x2,x3) & n_surfboard(x3) & a_white(s1) & Theme(s1,x3) & n_wave(x2) & Actor(e1,x1) & v_surf(e1) & n_person(x1))
exists p1 x1 x2 x3.((x1 = x2) & on(x2,x3) & n_surfboard(x3) & n_person(x2))