Doctors perform surgery on a patient.
Doctors performing heart surgery.
Surgery may be done in all parts of body, not only the heart.
exists e1 x1 x2 x3.(on(e1,x3) & n_patient(x3) & Theme(e1,x2) & Actor(e1,x1) & v_perform(e1) & n_surgery(x2) & n_doctor(x1))
exists e1 x1 x2 x3 x4.(a_topic(x1) & Theme(e1,x3) & Actor(e1,x2) & v_perform(e1) & n_surgery(x3) & of(x3,x4) & n_heart(x4) & (x1 = x2) & n_doctor(x1))