44Furthermore, the validity of such an approach is reinforced by the fact that it conforms to the general principle of legal certainty, since taking into account the costs and prices of the dominant undertaking enables that undertaking to assess the lawfulness of its own conduct, which is consistent with its special responsibility under Article 102 TFEU, as stated in paragraph 24 of this judgment. While a dominant undertaking knows its own costs and prices, it does not as a general rule know those of its competitors (Deutsche Telekom v Commission, paragraph 202).
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