A rebuttal (duplique) is a party's formal written response to the opposing party's reply in a judicial or arbitral proceeding — the fourth and typically final exchange of written submissions in an arbitration: request → response → reply → rebuttal. In financial valuation disputes, the rebuttal is the last opportunity to contest the opposing expert's methodology and conclusions before the hearing. It must be focused and technically precise: restating well-founded arguments, addressing the most significant methodological criticisms and presenting any additional market data supporting the retained approach.

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Example: in a post-acquisition valuation dispute, the seller's expert submitted a reply arguing that the buyer's DCF used an excessively high WACC of 11.5%. The buyer's rebuttal responds with three specific points: updated Duff & Phelps data supporting the size premium used, two additional comparable transactions supporting the beta selection, and a sensitivity analysis showing that even at 10.0% WACC the buyer's claim is supported. The rebuttal closes the written phase before the hearing.

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Hectelion prepares technically rigorous rebuttals in financial valuation arbitrations, addressing expert disagreements with precision and market evidence.