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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 receipt(df):
 """ Return a dataframe to verify if a item has a receipt. """

    mutated_df = df[['IdPRONAC', 'idPlanilhaItem']].astype(str)
    mutated_df['pronac_planilha_itens'] = (
        f"{mutated_df['IdPRONAC']}/{mutated_df['idPlanilhaItem']}"
    )

    return (
        mutated_df
        .set_index(['pronac_planilha_itens'])
    )