function navigation() 
{
hauteur=400;
largeur=750;
var winl = (screen.width - largeur) / 2;
var wint = (screen.height - hauteur) / 2;
winprops = 'height='+hauteur+',width='+largeur+',top='+wint+',left='+winl+',scrollbars=1,resizable'
fen = window.open ('',"popup",winprops);
if( self.focus ) fen.focus();
}