See the slides:
 http://ii.fmph.uniba.sk/cl/view/courses/1-AIN-625-lpp/1112zs/pr/doc/handout.pr05.pdf
See also the lecture notes from the previous year:
 http://ii.fmph.uniba.sk/cl/view/courses/1-AIN-625-lpp/1011zs/ln/doc/ch_p_sb.pdf