function $(node){
  return document.getElementById(node);
}

function navigate(e) {
	var code;
	if (!e) var e = window.event;
	if (e.keyCode) code = e.keyCode;
	else if (e.which) code = e.which;
        switch(code){
            case(37):
                var newLoc = $("previous").href;
                window.location = newLoc;
                break;
            case(39):
                var newLoc = $("next").href;
                window.location = newLoc;
                break;
        }
}
window.onkeyup = navigate;