Loopy / Slitherlink
Why does Loopy reject two separate loops?
The solution is one uninterrupted closed loop. Satisfying all numbered cells does not permit several loops or branches. Each used vertex must have exactly two incident loop edges.
Worked example
A square-grid clue 0 excludes all four surrounding edges. This local deduction still has to fit the final single loop.
What to check on your board
Apply the rule above to your current board, then verify the remaining puzzle constraints. The example explains a local deduction; it is not a solution to every randomly generated board.
Checking your next move
At a used vertex, count the incident edges before extending the line. A branch would exceed the required two. If a local section closes while other required edges remain outside, revisit that closure rather than accepting several separate loops.
Using this reference
For Loopy / Slitherlink, read the rule and the worked example together before opening the game. Separate what the rule explicitly requires from what only seems likely on the current board. A useful next move is one you can explain from the visible constraints, not merely a pattern that looks familiar.
If you get stuck, isolate a smaller part of the position and list what is still possible there. After a move, check the affected rows, regions or connections again. The reference explains the documented rules; progress, controls and save behavior belong to the linked game.
Read the developer’s manual ↗ · Open the developer’s browser version ↗
Manual inspected: · Simon Tatham & contributors · MIT