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Solve the following python programming problem given the following code:
def _resolve_rule_refs(self, grammar_parser, model_parser) : 
    'Resolves parser ParsingExpression crossrefs.' 
    resolved_set = set () 
    def resolve(node) : 
        '
            Recursively resolve peg rule references and textx rule types.

            Args:
                node(ParsingExpression or RuleCrossRef)
            ' 
        def _inner_resolve(rule) : 
            if grammar_parser.debug : 
                grammar_parser.dprint ('Resolving rule: {}'.format (rule)) 
initial_rule_name = rule.rule_name 
            if (type (rule) is RuleCrossRef) : 
                rule_name = rule.rule_name 
                if (rule_name in model_parser.metamodel) : 
                    rule = model_parser.metamodel [rule_name]._tx_peg_rule 
                    if (type (rule) is RuleCrossRef) : 
                        rule = _inner_resolve (rule) 
                        model_parser.metamodel [rule_name]._tx_peg_rule = rule 
else : 
                    (line, col) = grammar_parser.pos_to_linecol (rule.position) 
                    raise TextXSemanticError ('Unexisting rule "{}" at position {}.'.format (rule.rule_name, (line, col)), line, col) 
assert isinstance (rule, ParsingExpression), '{}:{}'.format (type (rule), text (rule)) 
            if (hasattr (rule, '_tx_class') and (len (rule._tx_class._tx_attrs) > 0)) : 
                rule._tx_class._tx_type = RULE_COMMON 
abstract = False 
            for (idx, child) in enumerate (rule.nodes) : 
                if (child not in resolved_set) : 
                    resolved_set.add (rule) 
                    child = _inner_resolve (child) 
                    rule.nodes [idx] = child 
if (rule.rule_name != initial_rule_name) : 
                    abstract = True 
else : 
                    if (rule.root and (not rule.rule_name.startswith ('__asgn')) and hasattr (child, '_tx_class') and isinstance (rule, OrderedChoice)) : 
                        abstract |= (child._tx_class._tx_type != RULE_MATCH) 
if abstract : 
                cls =...

    
    

    Fix the buggy line: if self.debug :
assistant
#Here is Python program to fix the buggy line: if self.

if grammar_parser.debug :