A man in a black shirt and jeans appears to be working on some piping system.
A plumber attempts to correct a problem with the plumbing system.
The first sentence doesn't say what type of man he is nor what type of piping system it is. Sentence 2 goes into more detail and used the descriptors plumber and plumbing. It also tells us that he isn't just working on the system, he's correcting a problem with it.
exists e1 p1 s1 x1 x2 x3 x4.(Topic(e1,p1) & Actor(e1,x1) & v_appear(e1) & exists e2 x5 x6.(on(e2,x5) & n_system(x5) & of(x5,x6) & n_piping(x6) & Actor(e2,x1) & v_work(e2)) & in(x1,x2) & subset_of(x4,x2) & n_jeans(x4) & subset_of(x3,x2) & n_shirt(x3) & a_black(s1) & Theme(s1,x3) & n_man(x1))
exists e1 p1 x1 x3 x4.(n_system(x3) & of(x3,x4) & n_plumbing(x4) & Topic(e1,p1) & Actor(e1,x1) & v_attempt(e1) & exists e2 x2.(Theme(e2,x2) & Actor(e2,x1) & v_correct(e2) & with(x2,x3) & n_problem(x2)) & n_plumber(x1))