function TabSet() {
  this.displayedTab = null;
  }

  TabSet.prototype.showTab = function(tabName) {
    if(this.displayedTab != null) {
	    document.getElementById(this.displayedTab).style.display = "none";
		  }
		    document.getElementById(tabName).style.display = "block";
			  this.displayedTab = tabName;
			  }