David Ganz Stamp

Stamps collector
Roni Kagan from Collect Forum website sent me this photo of an envelope with a Czechoslovakian stamp depicting Jewish

scientist David Ganz (1541-1613) tombstone in Prague which was the first Jewish tombstone, which carried on it the Star of David symbol; apparently because the title of Gans’ astronomy book was Magen David.

On the cancel we see a 'Swedish Hat' inside the Star of David - why?

In the mid 1600 Swedish forces attacked Prague and the Jews helped to defend the city for the emperor Emperor Ferdinand II.