ACKNOWLEDGEMENTS

Sources & privacy.

Puzzle data

The books contain selected positions from the Lichess open puzzle database, released under the Creative Commons CC0 public-domain dedication. The positions have been selected, reordered and checked for each workbook. These are independent publications and are not endorsed by Lichess.

Diagram artwork

Chess diagram pieces are by Colin M. L. Burnett (Cburnett), from the Wikimedia Commons chess piece set as distributed with python-chess, used under Creative Commons Attribution-ShareAlike 3.0. They are scaled and rendered in black and white; the piece shapes are unchanged. See the artwork source. This license applies to the piece artwork, separately from the original text and page designs.

Website privacy

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Book previews

The sample pages are selected previews from the workbooks. Original editorial text and page design © 2026 Ventsislav Vasilev, with separately licensed materials credited above.