anchor.diff:              self.WorkbookName = rf.WorkbookName &&
               self.WorksheetName = rf.WorksheetName &&
               self.FunctionName = rf.FunctionName
  +            // TODO: should also check ArgumentList here!
   
       and ReferenceConstant(wsname: string option, value: int) =
           inherit Reference(None, None, wsname)
  +        override self.Type = ReferenceType.ReferenceConstant
           member self.Value = value
           override self.ToString() = "Constant(" + value.ToString() + ")"
           override self.Equals(obj: obj) : bool =
  
positive.code: 
      and ReferenceFunction(wsname: string option, fnname: string, arglist: Expression list) =
          inherit Reference(None, None, wsname)
          member self.ArgumentList = arglist
          member self.FunctionName = fnname
          override self.ToString() =
  
negative.code: 
      and ReferenceString(wsname: string option, value: string) =
          inherit Reference(None, None, wsname)
          override self.Type = ReferenceType.ReferenceString
          member self.Value = value
          override self.ToString() = "String(" + value + ")"
          override self.Equals(obj: obj) : bool =
  