function showCourse(id) {
    
    $$('.course').each(function(elem) {
            if(elem.visible())
                Effect.BlindUp(elem, {duration: 0.5});
    });
    
    $$('.courselink').each(function(elem) {
            if(elem.hasClassName('active'))
                elem.removeClassName('active');
    });
    
    Effect.BlindDown('course_'+id);
    $('course_'+id).appear();
    
    $('courselink_'+id).addClassName('active');
    
    return false;
}

function nextLinkSet() {
    
    if(parseInt($('catpage').innerHTML) < parseInt($('totalpages').innerHTML)) {     
        $('catpage').update(parseInt($('catpage').innerHTML)+1);
        updateLinkSet()
    }
    
}

function previousLinkSet() {
    if(parseInt($('catpage').innerHTML) > 1) {     
        $('catpage').update(parseInt($('catpage').innerHTML)-1);
        updateLinkSet()
    }
}

function updateLinkSet() {
    
    var start = (parseInt($('catpage').innerHTML) - 1) * ELEMS_PER_CATEGORY;
    var end   = start + ELEMS_PER_CATEGORY;
    
    $$('.courselinkli').each(function(elem, index) {
                                if(index >= start && index < end) {
                                    elem.appear();
                                }
                                else {
                                    elem.hide();
                                }
    });
    
}