What are the hidden books in the grocery store?

The library had been compiled by members of the Bund - an adult socialist movement. Riva noted that books had been banned - all books. But those who were living in the ghetto had managed to compile a reasonable library. The problem was that there is a steady stream of people in and out of the library and it was time to move it from its location. The children agreed to have it in their new home, found some scraps of lumber for shelving and moved the three hundred books.