8. Position Libraries

A position library, as the name implies, is a collection of chess positions. At startup, Sigma Chess will load the standard “Sigma Library” which mainly contains opening lines/positions. However, a position library can also contain non-opening positions. In Sigma Chess 4 and earlier versions, the libraries were restricted to opening lines (hence they were called opening libraries), because they contained moves rather than positions.

When it's Sigma Chess's turn to move and it can play a move leading to a position stored in the library, it will bypass its normal search algorithm and play the move right away. If more than one move leads to a library position, Sigma Chess will pick one randomly. For instance in the initial position, Sigma Chess will choose randomly between the standard opening moves e2-e4, d2-d4, Ng1-f3 etc., because the resulting positions are all stored in the standard "Sigma Library".

You can select another library via the standard Open... command in the File menu, which then becomes the default library.

Sigma Chess includes a powerful built-in Library Editor which lets you create your own opening libraries as well as edit existing ones. This feature is not available in the Lite version, however.

Note: The position libraries are bypassed in the Infinite and Mate Finder levels.
 

The Library Editor

The Library Editor command opens a Library Editor window below the game record, which shows the stored continuations and the total number of positions in the library. Additionally, the editor commands are available as 3 buttons:
 

The example above shows the opening library editor for the position after white has played 1. e2-e4 in the initial position. If you click on one of the moves in the list, that move is automatically played and the move list is refreshed accordingly.

You don't need to open the Library Editor window in order to add a few positions, but it's recommended if you want to add many positions, such as opening lines: If the "Auto add new positions" checkbox is checked, you don't manually have to invoke the Add Position command after each move - when you play a move on the board, the new position is automatically added to the library.

You can create a new empty position library from scratch via the New Library... command. New moves can then be added as described above.