function show_btn_back() {
    var output = '';

    output += '<span class="button_back"><a class="but_back"></a></span>'+"\n";
    document.write(output);
}

function show_btn_print() {
    var output = '';

    output += '<span class="button_print"><a class="but_print"></a></span>'+"\n";
    document.write(output);
}

$(document).ready(function(){
    $('a.but_back').click(function(e){
        e.preventDefault();
        history.go(-1);
    });
    
    $('a.but_print').click(function(e) {
        e.preventDefault();
        window.print();
    }); 
});