.art_img_class {width:200px;background:#f0f0f0;margin-top:1em;font-size:0.7em;display:none;}
art_imgs = 0;
cur_art_img = 1;
function prev(){
for (i=1;i=art_imgs;i++){
document.getElementById("art_img_"+i).style.display = "none";
}
if(cur_art_img==1){
cur_art_img = art_imgs;
}else{
cur_art_img -= 1;
}
...