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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 get_model_index_properties(instance, index):
 """Return the list of properties specified for a model in an index."""

    mapping = get_index_mapping(index)
    doc_type = instance._meta.model_name.lower()
    return list(mapping["mappings"][doc_type]["properties"].keys())