The case notes
Reading an extra region
Each shaded extra region contains the digits 1 through 9 exactly once, in addition to the ordinary rows, columns and boxes. Watch a worked example, then try the idea in a puzzle.
Put it into practice
Shaded cells form an extra region
This shaded patch crosses the usual box borders. It is an extra region: another set of nine cells that needs every digit once.
1, 2, 4, 5, 6, 7, 8, 9 → missing 3
Inside the shading, we have one and two, then four, five, six, seven, eight and nine. Only three is missing.
r4c4 = 3
So this last shaded cell is three. Count the extra region just as you would count an ordinary box.
An extra set, with the same 1–9 rule
Rows, columns and boxes still apply. The shaded group simply adds another place where digits cannot repeat.
Read the transcript
This shaded patch crosses the usual box borders. It is an extra region: another set of nine cells that needs every digit once. Inside the shading, we have one and two, then four, five, six, seven, eight and nine. Only three is missing. So this last shaded cell is three. Count the extra region just as you would count an ordinary box. Rows, columns and boxes still apply. The shaded group simply adds another place where digits cannot repeat.
