anchor.diff:      } else {
           upControl.show(); downControl.show();
       }
  +}
  +
  +function updateDeleteControlVisibility(objectType, elts) {
  +    var controls = $$('.' + objectType + '-delete-control')
  +    if (elts.length <= 1) {
  +        controls.each(function(c) { c.hide() })
  +    } else {
  +        controls.each(function(c) { c.show() })
  +    }
   }
positive.code:     }
      href += objectType + '=' + objectId
      var a = Builder.node("a", {
          className: objectType + '-control control',
          id: objectType + "-" + objectId + "-" + controlName,
          href: href
      })
  
negative.code:     var siblings = $A(thisArm.parentNode.getElementsByTagName("LI"))
  
      updateMoveControlVisibility('arm', thisArm.id.split('-')[1], thisArm, siblings)
      updateDeleteControlVisibility('arm', siblings);
  }
  
  function updateAllArmsControlVisibility(epochId) {
      var armItems = $$('#epoch-' + epochId + '-arms li');
      armItems.each(updateArmControlVisibility)
  }
  
  function createStudyControls() {
  