It looks like that the core team included: Marian Rejewski, Henryk Zygalski ,Jerzy Różycki. These were the most talented students from prof. Zdzisława Krygowski

It looks like that the core team included: Marian Rejewski, Henryk Zygalski ,Jerzy Różycki. These were the most talented students from prof. Zdzisława Krygowski from UaM https://amu.edu.pl/ https://amu.edu.pl/ which is a university located in Poznan.