Original Printable Puzzle Kit puzzle and checked teaching state. Print A4 or Letter portrait; turn off browser headers/footers and inspect the preview. Each section is a separate page. Green cells identify the pattern; dashed cells and crossed candidate digits mark eliminations. Coordinates are also listed below.

Pencil marks: Before the deduction

Before the deduction for the Pencil marks example

r1c6 has only candidate 7. Place it and remove that digit from its peers. Seed: editorial-basics-1. Eliminations: r1c5 remove 7; r1c7 remove 7; r1c8 remove 7; r3c6 remove 7. The original givens have exactly one solution, checked with a separate exact-cover solver. Later candidate states include the recorded prior deductions.

Pencil marks: Marked deduction

Marked deduction for the Pencil marks example

r1c6 has only candidate 7. Place it and remove that digit from its peers. Seed: editorial-basics-1. Eliminations: r1c5 remove 7; r1c7 remove 7; r1c8 remove 7; r3c6 remove 7. The original givens have exactly one solution, checked with a separate exact-cover solver. Later candidate states include the recorded prior deductions.

Pencil marks: After the deduction

After the deduction for the Pencil marks example

r1c6 has only candidate 7. Place it and remove that digit from its peers. Seed: editorial-basics-1. Eliminations: r1c5 remove 7; r1c7 remove 7; r1c8 remove 7; r3c6 remove 7. The original givens have exactly one solution, checked with a separate exact-cover solver. Later candidate states include the recorded prior deductions.

Pencil marks: Original puzzle

Original puzzle for the Pencil marks example

Fill each row, column and box with digits 1–9 once each. Seed: editorial-basics-1. . The original givens have exactly one solution, checked with a separate exact-cover solver. Later candidate states include the recorded prior deductions.

Pencil marks: Matching solution

Matching solution for the Pencil marks example

r1c6 has only candidate 7. Place it and remove that digit from its peers. Seed: editorial-basics-1. Eliminations: r1c5 remove 7; r1c7 remove 7; r1c8 remove 7; r3c6 remove 7. The original givens have exactly one solution, checked with a separate exact-cover solver. Later candidate states include the recorded prior deductions.