ne sont pas à ce jour l'objet ou la cause d'un sinistre.
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are neither the subject nor the cause of any claim.

where objet, as is often the case in FR, is what would commonly be considered as the 'subject' in EN, and refers to the apartment that's being sold, and the ST is stating, for example, that there is no claim pending for insured damage to that property (eg: broken windows);

and cause, in both FR and EN, refers to situations where some other property (a neighbouring apartment, the communal staircase, etc.), has suffered insured damage originated by some failing related to the property that's being sold (eg: water from leaking pipe in the apartment seeps put and damages the carpet in the communal corridor).

IOW, the ST differentiates between claims designed to recoup the apartment vendor's own losses, and claims against the seller's insurance but designed to cover the losses of third parties caused by the apartment that's for sale.