Question juridique clé
Whether the deadline for paying the court-cost advance in case 2C_399/2013 should be restored under Article 50 BGG.
Solution extraite
No restoration was warranted because the asserted financial difficulties were known before expiry of the deadline and could have been raised in time; the prior refusal to extend the Nachfrist cannot be revisited.
Motifs extraits
Restoration requires an unforeseeable, non-fault cause preventing timely action. Circumstances existing before expiry of the deadline must be invoked before expiry, and payment difficulties must be substantiated in time. The later explanations could and should have been raised already in the extension request.