# :param tax_system: Atributo requerido para incorporar la clave del régimen del contribuyente emisor al que aplicará el efecto fiscal de este comprobante.
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# """
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# self.signer = signer if isinstance(signer, Signer) else None
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# self.certificate = signer
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# self.rfc = rfc or signer.rfc
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# self.legal_name = legal_name or signer.legal_name
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# self.tax_system = tax_system
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# self.certificate_number = certificate_number or (signer.certificate_number if signer else "")