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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def is_builtin_variable(id_node):
 # type: (Dict[str, Any]) -> bool """ Whether the specified node is a builtin identifier. """

    # Builtin variables are always IDENTIFIER.
    if NodeType(id_node['type']) is not NodeType.IDENTIFIER:
        return False

    id_value = id_node['value']

    if id_value.startswith('v:'):
        # It is an explicit builtin variable such as: "v:count", "v:char"
        # TODO: Add unknown builtin flag
        return True

    if is_builtin_function(id_node):
        return True

    if id_value in ['key', 'val']:
        # These builtin variable names are available on only map() or filter().
        return is_on_lambda_string_context(id_node)

    # It is an implicit builtin variable such as: "count", "char"
    return id_value in BuiltinVariablesCanHaveImplicitScope