A man is doing some kind of maintenance work on a train.
A person is doing maintenance on a thing.
A man is a person and a train in a broad concept is a thing.
exists e1 x1 x2 x3 x4 x5.(Theme(e1,x2) & Actor(e1,x1) & v_do(e1) & of(x2,x3) & on(x3,x5) & n_train(x5) & n_work(x3) & of(x3,x4) & n_maintenance(x4) & n_kind(x2) & n_man(x1))
exists e1 x1 x2 x3.(on(e1,x3) & n_thing(x3) & Theme(e1,x2) & Actor(e1,x1) & v_do(e1) & n_maintenance(x2) & n_person(x1))