anchor.diff:  
   import java.util.*;
   import queries.*;
  -import expressions.*;
  +import expressions.bool.*;
  +import expressions.comparison.*;
   }
   
   @members {
  
positive.code:     :   '.'
      ;
  
  EQUALS
      :   '='
      ;
  
  QUOTES
  
negative.code:     ;
  
  joinStatement
      :   secondLevelId EQUAL secondLevelId
      ;
  
  secondLevelId returns [SecondLevelId result]
  