function shift_pic(x) {
  var y=x.id;
  y=y.replace('gallery_pic_','');
  if(isNaN(y)){alert('nan');return false;}
  y=Number(y);
  if(y<0||y>=tpics.length) {alert('out of range');return false;}
  document.getElementById('gallery_rollover').src=lpics[y];
}