Simple coloring: trap

A worked example

This position comes from SudokuByte’s lesson on the Simple coloring: trap. Gold cells hold the evidence; green cells are the pattern’s ends.

1. Where to look

   Build a connected two-color network, then inspect candidates outside it.

   Color one digit along connected strong links using alternating colors. A candidate that sees both color groups cannot be true.

2. Read the evidence in this position

   For digit 1, connected strong links produce two alternating groups. Teal: r5c7. Gold: r5c8.

3. Why the deduction must follow

   One entire color group is true and the other false, within this connected component. An uncolored 1 seeing a member of each group is excluded either way.

4. Apply the result

   Erase 1 from r6c8. The pattern may remove candidates without immediately solving a cell.