1. Cross Lights study 1
1 steps in the included checked route. Try the board first, then compare the reasoning.
PRACTICE COLLECTION
Predict a press before making it
Compare corner, edge and interior crosses, then simplify repeated presses. Judge the predicted light pattern separately from the number of moves used.
Print these three studies with answers
Start with a decision
TRY IT 1 · lights-toggle-1
| C1 | C2 | C3 | C4 | C5 | |
|---|---|---|---|---|---|
| R1 | |||||
| R2 | |||||
| R3 | |||||
| R4 | |||||
| R5 |
What can you justify?
In the toggle sandbox, apply R1C1. Will R2C2 be on or off afterwards?
Written explanation
R2C2 starts off and is toggled 0 times. An even number leaves it as it began, so it finishes off. Diagonals do not belong to a press’s cross.
TRY IT 2 · lights-cancellation-1
| C1 | C2 | C3 | C4 | C5 | |
|---|---|---|---|---|---|
| R1 | |||||
| R2 | |||||
| R3 | |||||
| R4 | |||||
| R5 |
What can you justify?
In the toggle sandbox, apply R3C3 then R3C3. Will R3C3 be on or off afterwards?
Written explanation
R3C3 starts on and is toggled 2 times. An even number leaves it as it began, so it finishes on. The two identical presses cancel as light operations, even if an intermediate sandbox board is dark.
Apply the ideas to a complete board
These are fixed original studies, not new daily puzzles. The three study links below and this collection’s printable pack use identical starting positions. Their checked solution routes are included on each practice page. A collection’s technique drills may also appear in its lessons.
2. Cross Lights study 2
1 steps in the included checked route. Try the board first, then compare the reasoning.
3. Cross Lights study 3
2 steps in the included checked route. Try the board first, then compare the reasoning.