Reasoning · Learning guide

Separate a deduction from a guess

A deduction follows from the constraints. A guess proposes a possibility that still needs testing.

Write the reason

Before placing a digit, ask why alternatives are impossible. “It looks right” is a weaker justification than “every other position in this box conflicts with the row.”

Track assumptions

In harder puzzles, a trial assumption can be useful if you record it and undo all dependent steps on contradiction. Do not treat tentative values as established clues.

Enjoy a small finish

Speed is optional. A consistent method often makes a puzzle more satisfying than repeated blind changes. Use the check button as feedback after working through the constraints.

Further reading: Reference source ↗. Written for this starter collection. Check primary references for specialised use.