Additional explanations and context for select points in Books 1–3, based on feedback from early advanced review copy readers.
Some of my early readers who have received my advanced review copies have asked me a few questions about certain aspects of Books 1, 2, and 3. Here is a list of clarifications to their questions and confusion.
I will update this page with more information once people have raised more questions for me.
1) Book 2’s Parity Statement on Singles and Doubles (80% Rule)
Book 2 wrote a part where I said there is around an 80% chance for singles and doubles to alter parity. However, I did not show further examples of such.
Why I Say, “About 80%” Instead of 100%
When you clear a single or triple, the falling blocks above often shift the overall parity (odd/even pattern) of the field — especially when colored upstack meets garbage lines. In most cases, these clears reverse the parity, but rare situations — like when nothing falls down after the clear — leave parity unchanged. From experience, this happens roughly 20% of the time, so “about 80%” is a practical estimate.
Special Note on T-spins
T-spins affect parity in their own way. If a single or triple is made without the T piece causing the clear, parity usually changes — but since T placements themselves can change parity, the effects can sometimes cancel out. Therefore, not every single or triple alters parity.
For practical purposes of not overwhelming the reader, I did not elaborate on such, keeping the chapter concise.
I wrote more about this here (not for the faint-hearted!):
Credits to HelloKat for pointing this out.
2) Book 2’s Opener Chances (Mirrored Setups)
Someone suggested that certain opener chances are slightly inaccurate. This arises because of differences in methodology and assumptions used:
Opener Usability Methodology
I tested 100 random starting sequences and, in each case, recorded which opener was the best fit — rather than testing 100 sequences for each opener individually, as that would need 1000+ tests for 10 openers, which is not viable! This approach can understate some percentages because of overlaps.
Also, mirrored versions of openers were not counted, which halves the stated probability (e.g., a listed 12.5% would be 25% if mirrors were included). Thus, for Hachispin, I use only the version where the T-spin cavity is on the right side.
Credits to Hanola for pointing this out.
How to Tetris 