A parasurfer is airborne over the water.
Someone is parsurfing.
The " parasurfer " was the specific " Someone " explained in the second sentence.
exists s1 x1 x2.(n_water(x2) & over(s1,x2) & Theme(s1,x1) & a_airborne(s1) & n_parasurfer(x1))
exists p1 x1.(exists x2.((x1 = x2) & n_parsurfing(x2)) & n_person(x1))