The current version of Spear was rewritten from scratch in 2006, and based
on the open source chess program Crafty. Its datastructures (bitboards and
search tree representation) are taken from Crafty and are therefore very
close to Bonanza, which also has used Crafty. As far as programming
structure is concerned, Spear is very similar to Bonanza, using full-width
search, which is the common search method for chess programs. Despite being
similar, it is important to understand that the basic programming structure
of Spear was already fixed before the source code of Bonanza was made
available and Spear can therefore not be considered to be using the Bonanza
library.

This being said, because of the similar program structure, Spear has
benefitted from a number of ideas in Bonanza, using a number of search ideas
(including futility pruning) and the so-called "Bonanza Method" for tuning
the evaluation function features. However, the evaluation function used in
Spear is completely different from Bonanza, and Spear has also some extra
search tools that are not in Bonanza, like a df-pn tsume solver.