A few years ago Nell could have relied on it. But in recent years the 
Primer had become much subtler than it used to be, full of hidden traps, and 
she could no longer make comfortable and easy assumptions. It was just as 
likely that this chain had descended straight from the throne room itself, and 
that the mechanical Duke was, for some unfathomable reason, trying to dupe her. 
So while she was happy to respond to this message in kind, she intended to take 
a guarded approach until she had established whether the sender was human or 
mechanical.