These six books are roughly arranged by difficulty. The second and third may be somewhat unique—some parts might even be simpler than the first, but the first book is foundational.
If you're at Step 2-3 level, start with the first book: Chess Tactics for Beginners.
If you're at Step 3-4 level, start with the fourth book: 1400-1600.
If you're at Step 4-5 level, start with the fifth book: 1600-1800.
If you're at Step 5-6 level, go directly to the sixth book: CT*Art 4.0
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