function keyNavigation(event){
	if(event.keyCode == 37 && document.getElementById("prev_page") != undefined)
		window.location.href = document.getElementById("prev_page").href;
	if(event.keyCode == 39 && document.getElementById("next_page") != undefined)
		window.location.href = document.getElementById("next_page").href;
}

window.onkeydown = keyNavigation;