The Quiet Grid, Issue 4: Hidden in Plain Sight

Issue 3’s lonely candidate lived in row 5, column 6, and it was a 2. A tip of the cap to the quick eyes. Now for the sneakier cousin of the naked single.

Three squares

One. A hidden single hides among candidates. Pick a digit and a unit, say a 7 and a column. Look at every empty square in that column and ask: can a 7 go here? If a 7 already sits in that square’s row or box, the answer is no. Very often, every empty square gets a no except one, and that one square must be the 7, even if its pencil marks show two or three other possibilities. The digit was hiding in plain sight. Lovely, is it not?

Two. The quiet of a house after everyone has gone to bed. Dishes done, one lamp on, the refrigerator humming its one note. It is the best solving light there is, and it costs nothing.

Three. Behind the grid: every puzzle we make has a permanent name, a little serial number that never changes, and we keep a ledger of every book it has ever appeared in. If a puzzle ever shows up in a second book, the ledger knows, and so will you, because we will say so. No quiet recycling. Every page you paid for is accounted for.

Two voices

And he said, My presence shall go with thee, and I will give thee rest. — Exodus 33:14

Chapter five of Bible Verse Sudoku is called Peace and Rest, and this verse opens it. We chose it for this issue on purpose, since the days are getting shorter and the lamp is coming on earlier.

From your replies: [two reader one-day records with first names and permission, placeholder]. This issue’s question is a gentle either-or: which do you spot first when you sit down, naked singles or hidden ones? There is no wrong answer, and we suspect the split is closer than anyone thinks.

One grid

Column 3 in this grid is missing its 7. Several of the empty squares in that column could hold other digits, but only one of them can hold the 7. Which row?

.  8  . | 4  9  . | 7  .  .
.  .  2 | 1  .  6 | .  5  8
.  .  . | 7  .  . | .  .  9