Just saw this thread of a couple of months ago, so my apologies for returning to it so late. As it happens, my grandfather, Thomas Zielinski, owned the Scottish Cafe (Brettschneider was the manager). I recently wrote a couple of papers that answer many of the questions raised in the discussion - the full text of the English "Mathematicians at the Scottish Cafe" is here: https://www.researchgate.net/publication/335742570_Mathematicians_at_the_Scottish_Cafe). I am currently embarking on a play loosely around this topic.