var back_button = {
    related_button: null,

    init: function() {
        if(!document.getElementById || !document.getElementsByTagName) return;

        this.related_button = document.getElementById('button_back');
        if(!this.related_button) return;
        this.related_button = this.related_button.getElementsByTagName('input')[0];
        Event.observe(this.related_button, 'click', this.clickListener.bindAsEventListener(this), false);

    },

   clickListener: function(e) {

        var event = window.event ? window.event : e;
        var eventTarget = event.srcElement ? event.srcElement :  event.target;
        if(eventTarget.nodeName.toLowerCase() == 'img') {
            eventTarget = eventTarget.parentNode;
        }

        if(window.event) {
            window.event.cancelBubble = false;
            window.event.returnValue = false;
        } else {
            e.stopPropagation();
            e.preventDefault();
        }
        if(ie6 || ie7) {
            var current_location = window.location
            document.location = current_location;
        } else {
            history.go(-1);
        }

   }

}