<instance>
   <presentation name="?" format="XCSP 2.0 for CSU670"/>
   <variables nbVariables="4">
   </variables>
   <relations nbRelations="1">
     <relation name="1in3" number="22">
     // one in three
     </relation>
   </relations>
   <constraints nbConstraints="3">
      // reference must be to relation name
      <constraint scope="V0 V1 V2" reference="1in3"/>
      <constraint scope="V0    V2 V3" reference="1in3"/>
      <constraint scope="V0 V1    V3" reference="1in3"/>
   </constraints>
</instance>
