Men are working by a cement mixer.
Men are at work fixing a problem with the cement mixer.
You can not infer there is a problem.
exists e1 x1 x2 x3.(by(e1,x2) & n_mixer(x2) & of(x2,x3) & n_cement(x3) & Actor(e1,x1) & v_work(e1) & n_man(x1))
exists e1 p1 x1 x2 x3 x4.(n_mixer(x3) & of(x3,x4) & n_cement(x4) & for(p1,e1) & Theme(e1,x2) & Actor(e1,x1) & v_fix(e1) & with(x2,x3) & n_problem(x2) & exists x5.(at(x1,x5) & n_work(x5)) & n_man(x1))