function cambiaImg(par){
    if(par == "1"){
    document.getElementById("img").innerHTML = "<a href=\"http://www.internetbookshop.it/ser/serdsp.asp?isbn=8842074241\"><img src=\"Immagini/cover_montanari.jpg\" border=\"0\" alt=\"Copertina - Massimo Montanari\" /></a>";
    }
    if(par == "1.2"){
    document.getElementById("img").innerHTML = "<a href=\"http://www.internetbookshop.it/ser/serdsp.asp?shop=1&c=BBB46NQQUU5BB\"><img src=\"Immagini/cover2_montanari.jpg\" border=\"0\" alt=\"Copertina - Massimo Montanari\" /></a>";
    }    
    if(par == "2"){
    document.getElementById("img").innerHTML = "<a href=\"http://www.internetbookshop.it/ser/serdsp.asp?isbn=8806178288\"><img src=\"Immagini/cover_petrini.jpg\" border=\"0\" alt=\"Copertina - Carlo Petrini\" /></a>";
    }
    if(par == "3"){
    document.getElementById("img").innerHTML = "<a href=\"http://www.internetbookshop.it/ser/serdsp.asp?isbn=8851521964\"><img src=\"Immagini/cover_claudelevis.jpg\" border=\"0\" alt=\"Copertina - Claude Levis-Strauss\" /></a>";
    }        
}