55In those circumstances, in order to ensure compliance with the principle of effectiveness, if the national court finds that the fact of requiring a pharmaceutical laboratory such as Boiron to prove that wholesale distributors are overcompensated, and thus that the tax on direct sales amounts to State aid, is likely to make it impossible or excessively difficult for such evidence to be produced, since inter alia that evidence relates to data which such a laboratory will not have, the national court is required to use all procedures available to it under national law, including that of ordering the necessary measures of inquiry, in particular the production by one of the parties or a third party of a particular document.
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