function go(step) {
          if (document.getElementById('slideProj').disabled || step == 0) return;
          var jl = document.getElementById('jumplist');
          var cid = 'slide' + snum;
          var ce = document.getElementById(cid);
          if (incrementals[snum].length > 0) {
                  for (var i = 0; i < incrementals[snum].length; i++) {
                          removeClass(incrementals[snum][i], 'current');
                          removeClass(incrementals[snum][i], 'incremental');
                  }
          }
          if (step != 'j') {
                  snum += step;
                  lmax = smax - 1;
                  if (snum > lmax) snum = lmax;
                  if (snum < 0) snum = 0;
          } else
                  snum = parseInt(jl.value);
          var nid = 'slide' + snum;
          var ne = document.getElementById(nid);
          if (!ne) {
                  ne = document.getElementById('slide0');
                  snum = 0;
          }
          if (step < 0) {incpos = incrementals[snum].length} else {incpos = 0;}
          if (incrementals[snum].length > 0 && incpos == 0) {
                  for (var i = 0; i < incrementals[snum].length; i++) {
                          if (hasClass(incrementals[snum][i], 'current'))
                                  incpos = i + 1;
                          else
                                  addClass(incrementals[snum][i], 'incremental');
                  }
          }
          if (incrementals[snum].length > 0 && incpos > 0)
                  addClass(incrementals[snum][incpos - 1], 'current');
          ce.style.visibility = 'hidden';
          ne.style.visibility = 'visible';
          jl.selectedIndex = snum;
          currentSlide();
          number = 0;
  }