localized Record.decode_type: use standard Proof_Context.get_sort;
clarified Record.varifyT: more convential use of maxidx + 1;
By chapter:
chapters 1 and 2, maybe 3: Peter White
chapters 6, 7 and 8: David von Oheim
chapter 6, maybe 8: Gerwin Klein
chapters 3, maybe 4: Tanja Vos
chapters 1-3 at least: Stefano Bistarelli