The man is welding the iron.
The iron is hot.
Just because iron is being welded means that it is hot because it is being welded. The iron may have be hot for some other reason.
exists e1 x1 x2.(n_iron(x2) & n_man(x1) & Theme(e1,x2) & Actor(e1,x1) & v_weld(e1))
exists s1 x1.(n_iron(x1) & Theme(s1,x1) & a_hot(s1))