## 11 September 2010

An interesting class of chess960 start positions (SPs) has the first five pieces in the same order found in the traditional SP: 'RNBQK***'. Logic says that there should be four such positions. Since the White Bishop starts on a dark square, the other Bishop must be on one of the remaining light colored squares, f1 and h1. For each of these possibilities, the Rook and Knight can be switched on the remaining two squares. Searching the list of all 960 SPs identifies the following SPs as belonging to this class. (The twin of each SP is given in parentheses).
518 RNBQKBNR (534 RNBKQBNR)
519 RNBQKNRB (530 BRNKQBNR)
614 RNBQKBRN (246 NRBKQBNR)
615 RNBQKRNB (242 BNRKQBNR)

Using similar logic, there are four positions that fit the pattern '***QKBNR'. They are shown in the following table.

226 BNRQKBNR (631 RNBKQRNB)
230 NRBQKBNR (630 RNBKQBRN)
514 BRNQKBNR (535 RNBKQNRB)
518 RNBQKBNR (534 RNBKQBNR)

By definition, the well known SP518 RNBQKBNR appears in both tables. What makes these positions interesting is that a majority of the pieces can follow the development patterns known from SP518. Last year I had the opportunity to play one of these positions and the game evolved as shown in the following diagram.

SP514 BRNQKBNR
After 4...Bf8-e7

My opponent outrated me by several hundred points and I was surprised to see how he conducted the opening. While I followed classical opening principles, his moves fit into some other pattern of logic. It was one of the games that gave me the inspiration for two posts on this blog: Extravagant Openings in Chess960 and Extravagant Openings (cont.).

White's neglect of the center in the early moves -- 1.b4 d5 2.f4 Nf6 3.e3 e6 4.Nf3 Be7 (diagram) -- is striking. The game continued 5.Bb5+ c6 6.Bd3. I had already decided that the move ...c6 would be necessary before ...b6, in order to prevent the cramping b4-b5. When White forced this move by 5.Bb5+, I was convinced that I had won a tempo and was happy with the position. The game was eventually drawn after 66 moves.