In the template of dom-repeat that the expression doesn’t succeed

Question

 <dom-repeat id="xRepeat" as="x">
         <template is="dom-repaet">
             <div>
                 <dom-repeat  items="[[x]]" as="y">
                     <template is="dom-repaet">
                         <div>
                             <dom-repeat  items="[[y]]" as="z">
                                 <template is="dom-repaet">
                                     <span  checked-data-id="{{x*y*z}}" >
                                        {{z}}
                                     </span>
                                 </template>
                             </dom-repeat>
                         </div>
                     </template>
                 </dom-repeat>
             </div>
         </template>
     </dom-repeat>

"{{xyz}}" is no response in Polymer#2.0.

What can I do to make it work? ? ? ? ? ( @ @ ) I'm feeling ( < ) ...