A man is sitting on the ground welding something.
A person is working on something with a welding torch.
Just because he is welding something doesn't mean he is using a welding torch.
exists e1 e2 x1 x2 x3 x4.(n_ground(x2) & on(e1,x2) & Theme(e2,x4) & Actor(e2,x3) & v_weld(e2) & n_thing(x4) & (x2 = x3) & Actor(e1,x1) & v_sit(e1) & n_man(x1))
exists e1 x1 x2 x3 x4.(on(e1,x2) & with(x2,x3) & n_torch(x3) & of(x3,x4) & n_welding(x4) & n_thing(x2) & Actor(e1,x1) & v_work(e1) & n_person(x1))