A bilateral declaration without material acts is sufficient for the transfer of possession:
Civil Code
2015 English source edition · Current applicability not established.
This is the 2015 English-language edition attributed in its front matter to the Ministry of Justice. Eri Atlas has not independently verified the translation, later changes, or whether the text is currently in force. Nine passages are incomplete in the available scan and are identified where they occur.
Article 973
Constructive Possession · Preserved transcription; page attribution imported from the source collection. Verify against the original.
where the transferor possesses the property and henceforth holds it for the acquirer by virtue of a stipulation made at the time of delivery;
where the acquirer was holder of the property for the transferor; and
where a third party held the property for the transferor and holds it for the recipient after the transfer. In this event possession does not pass until the third party has acknowledged the transfer or has been notified of it by the transferor or acquirer.
Nothing in this Article shall affect the rights of the creditors of the person exercising actual control over the property in the event of his bankruptcy, unless they knew or should have known that this person was not the owner of the property.