The Quiet Grid, Issue 3: The Naked Truth

Issue 2’s center square was a 1, and the reasoning is in last Monday’s note if you want to see it laid out. A tip of the cap to everyone who scanned their way there. Now, pencils out. This issue we write in the margins.

Three squares

One. A naked single is a square that shows you its own answer. Once you have penciled in the candidates for a few empty squares, look for the one with only a single small number left in it. That square is not hiding anything. It is naked, in the polite Sudoku sense of the word, and it is the next thing you fill in. Train your eye to check the squares with the most filled neighbors first; that is where naked singles like to live.

Two. Eraser crumbs are proof of thinking, not failure. A clean page means you never tried anything. A page with a few pink smudges means you were in the fight. Brush them off with the side of your hand and carry on. (Onto the floor. We will not tell.)

Three. Behind the grid: every puzzle we have ever made has been checked, independently and by machine, to have exactly one solution. All 610 of them. We ran the sweep again last month for the pleasure of watching it come back clean. When you finish one of ours, there was only ever one way it could end, and you found it.

Two voices

So teach us to number our days, that we may apply our hearts unto wisdom. — Psalms 90:12

Chapter three of Bible Verse Sudoku is called Wisdom for the Daily Walk, and this is its opening verse. Numbering, applying, a daily walk: it is a chapter a Sudoku book was always going to love.

Your voice, this issue: what is the most puzzles you have ever solved in one day, and where were you when it happened? Airport benches and waiting rooms are expected. Surprise us. Reply to the email or tell us on Facebook.

One grid

The middle box of this grid has four empty squares, marked a, b, c, and d, and we have penciled the candidates in for you:

.  2  . | .  7  . | .  .  .
.  8  9 | .  .  1 | 4  .  6
1  4  . | .  9  . | .  .  .
--------+---------+--------
.  .  4 | 7  5  3 | .  6  .
6  .  5 | 8  a  b | 3  9  7
.  .  . | c  d  9 | .  .  4
--------+---------+--------
.  .  . | 1  .  . | 6  .  .
.  .  . | .  6  5 | .  .  .
.  .  . | .  .  4 | .  7  2

Square a can be 1, 2, or 4. Square b can be 2. Square c can be 2 or 6. Square d can be 1 or 2. One of those four squares has a single candidate. Which square is it, and what goes there? Say it out loud if you like. It is very satisfying.

Answer next Monday, gently, as always.

New this week: we are on Pinterest, and the first thing we pinned is a set of free printable blank Sudoku grids in four layouts, for the evenings when you want to copy a puzzle out of the paper onto something roomier.