(b) While a game is in progress you may not refer to chess engines, chess computers or be assisted by a third party. Endgame tablebases may not be consulted during play but you may reference books, databases consisting of previously played games between human players, and other pre-existing research materials.
So the short answer is yes; and I use both chessgames.com and chesslive.de
But there's a catch: chessgames.com contains a very small percentage of games played by computers. The percentage is so small that only once have I stumbled across one. I continue to use this database, however, since I believe the percentage to be so small that the database as a whole ought to be acceptable.
I would welcome an authoratitive ruling on this.
Failing that, if chessgames.com is not acceptable then can anyone recommend an openings database that is guaranteed to be 100% human?
So we can use the opening databases during play then? The excerpt from the rules presented during login did not include the part of the phrase about referencing pre-existing material, I don't think, or I didn't read it properly. But it is still in the terms.
I frequently consult the opening books because it helps me not to stuff up the games until much later.
Unfortunately the index behind the games explorer is still a case-insensitive index by FEN. That is, it doesn't know the difference between a white pawn and a black pawn.
This is explained on page 7 of the Games Explorer thread Thread 57414. As a quick demonstration try the "cxd4" link here:
This kind of thing is surely going to make the percentage statistics unreliable as soon as any pawns reach the fifth rank. The same bug affects www.gensunasumus.com and caused me a lot of grief when I was using that site in 2005/2006.
But once that's been fixed it will be a strong contender.