- Verified positions
- 192 of 199 positions were checked move by move against the Syzygy tablebases. The rest were checked with Stockfish.
- Live checking
- When you play a move that is not the book move, Lucena asks the tablebase whether it still wins or holds. If it does, it is accepted.
- You play, not watch
- Each lesson is one idea and a replayable line. Then you play the position against a perfect defender.
- Spaced repetition
- FSRS schedules reviews. A flawless rep pushes a position weeks out. A slip brings it back tomorrow.