getUnion: function(params, diff, neededItems, cachedItems){
// using the diff, re-construct everything
return {data: canSet.getUnion(diff.needed, diff.cached, getItems(neededItems), getItems(cachedItems), this.algebra)};
},
return this.getListData(getSet).then(function(setData){
self.updateSet(setDatum, canSet.getUnion(getSet, set, getItems(setData), items, self.algebra), union);
});