Pietje Polak-de Vries was the sister of Aron de Vries.
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A Jokos file (number 54277) on this person can be at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.
This person is commemorated on a memorial in Harlingen. More information on this memorial can be found (in Dutch) on the website of the Nationaal Comité 4 en 5 mei.