Permissible resoruces in Daily Chess games?

As has been said before DB, opening books are legal.  So is moving the pieces around to analyse the position.  I've played correspondence chess for years.  Usually only against players I know.  I've been playing one friend for close to 10 years now.  He alway always always plays 1.c4.  I likewise play 1.e4.  We know exactly how each other plays but even with books never usually go more than 10 moves into book.  Likely less.  It's never been a significant advantage one way or another if one is looking at the position thoroughly.  I've had games last 6 months.  It is unreasonable to expect that We will not study chess in the 14 days between some moves.

The rules for correspondence chess are as likely to change as the rules for castling. 

in live chess you cannot. only in daily chess