anchor.diff:      var siblings = $$('div.epoch')
   
       updateMoveControlVisibility('epoch', thisEpoch.id.split('-')[1], thisEpoch, siblings)
  -    updateDeleteControlVisibility('epoch', siblings)
  +    updateDeleteControlVisibility('epoch', siblings, 'epochs')
   }
   
   function updateAllEpochsControlVisibility() {
  
positive.code:     }
  }
  
  function updateDeleteControlVisibility(objectType, elts) {
      var controls = $$('.' + objectType + '-delete-control')
      if (elts.length <= 1) {
          controls.each(function(c) { c.hide() })
      } else {
  
negative.code:     var siblings = $A(thisArm.parentNode.getElementsByTagName("LI"))
  
      updateMoveControlVisibility('arm', thisArm.id.split('-')[1], thisArm, siblings)
  }
  
  function updateAllArmsControlVisibility(epochId) {
      _updateAllArmsControlVisibility('epoch-' + epochId + '-arms')
  }
  
  function _updateAllArmsControlVisibility(eltId) {
      var armItems = $$('#' + eltId + ' li');
      armItems.each(updateArmControlVisibility)
      updateDeleteControlVisibility('arm', armItems, eltId);
  }
  
  function createStudyControls() {
  