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Spur Loop

Updated on (created ) — Filed under: 90 List Naoki Inaba Paper Ported Puzzle crossing loop monoline
Draw a (possibly) crossing loop through all tiles, with segments of length at least 2.

Based on ruleset by Naoki Inaba

First seen (2011) at PuzLab

This is an example puzzle - tap to interact!

Draw a single, possibly crossing, closed loop.

The loop may not visit absent tiles.

The loop may not branch.

The loop must visit all empty tiles.

Each loop segment must be at least length 2.

Solved!
Rule panels by PinkHoodie on 22/03/2025

Naoki Inaba composed the ruleset and first puzzles of Spur Loop (2011), shared at PuzLab, , alongside many other original paper puzzles. This ruleset is also known as Spool Loop, Shupururupu and Cross Loop.

In 2023 Pedro released the Spur Loop interactive app, leveraging the Kudamono Editor system. Pedro derived the programming logic, decided on colours & input modes and created all graphic assets, by tracing SVG paths. Rule panels by PinkHoodie on 22/03/2025.

All puzzles listed on this page have a single, unique solution. Brand-new puzzles are proudly submitted by their authors regularly, while historic puzzles gain a new life in the interactive Kudamono format: here transcribed for the first time, with permission from each author, on a unit-, genre- or general basis.

Example:

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Puzzles:

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Start with a blank page (new Spur Loop puzzle).

Detailed editing instructions and shortcuts can be found at the manual.

The following variants are suggested: unequal-lengths, directions, hex, kiki, non-consecutive-lengths and vertigo.

For more information about global variants, and how to combine multiple variants in a single puzzle, please see the variants page.

The following custom insertion shortcuts apply to Spur Loop:

Keyboard shortcuts for Spur Loop (S = solving, E = editing, S/E = both solving and editing )
Glyph When Submode Shortcut Description
www.w3.org/2000/svg'> S—-A → Uauto mode: auto-choose submode based on gesture type and location
www.w3.org/2000/svg'> SlineL → Iline (solve): drag or click to draw definitive line (solve)
www.w3.org/2000/svg'> EsymbolXAbsent tile: click or drag to place definitive symbol Absent tile
www.w3.org/2000/svg'> S/Eaux markPShade positive: click or drag to place auxiliary Shade positive
www.w3.org/2000/svg'> S/Eaux markNShade negative: click or drag to place auxiliary Shade negative
www.w3.org/2000/svg'> S/Eaux markXcross: click or drag to place auxiliary cross
www.w3.org/2000/svg'> S/Eaux lineS → Ksketch line: drag or click to sketch auxiliary line

Pressing an exclusive editing shortcut while solving, or vice-versa, causes a switch into that context. In contrast, shared shortcuts cause no switch, but are instead chosen to match the current context.

To copy the right url, simply follow the button sequence (export) → (link).

Likewise, a puzzle image may be exported via (export) → (picture).

Made a puzzle that you'd like to list here at Pedro's Works? Simply follow the Submission Guide!

When sharing a Spur Loop link on other social networks or across the fediverse please also include the hastag #KudamonoEditor in the post. Including the puzzle picture will usually enhance your post.

This table lists external sites and databases referencing Spur Loop.

Interlinks - other sites and databases listing this puzzle genre
Site Link Comment
Janko.atSpur Loop pageOtto Janko has a page for Spur Loop. These pages often include an interactive applet for puzzle solving.
PuzzleSquareJPSpur Loopyou may also share your Spur Loop puzzles at PuzzleSquareJP: please include the hashtag #KudamonoEditor in the puzzle description

Please with any issues and suggestions.

There are specific instructions for live conflict highlighting and input issues, for improving the rule panels or reporting non-uniquenesses.

For any other bugs, please:

  • describe what you were trying to do,
  • what happened instead, and
  • send the current url (plus any visible error logs and possibly, supplementary screenshots).

You may check whether your bug is already covered by the unit tests (it may take a few seconds before the page loads fully). Any yellow boxes indicate a failed test. "Performance issues" currently indicate all passed tests, slow or not.

If you find a situation where the live conflict highlighter is not working as you'd expect (e.g. too aggressive, incorrect), please send a small test case url plus a brief explanation of what should be happening instead.

A good test case includes the smallest possible board, with the fewest possible elements, that is still able to unambiguously reproduce the issue.

For interface issues related input modes, or more generally to clicking/touching/dragging, keyboard shortcuts, etc… please submit an input test case, as detailed in the Inputs Initiative.

For simple typos/rewordings, a short email suffices. For more substantial changes, please refer to the rule panels guidelines.

If you find a non-uniqueness in one of the puzzles, please first check whether you are able to contact the puzzle author directly to request a fix.

If that seems impractical, please submit either:

  • a corrected, unique puzzle url (with solution), if you are able to suggest a fix (preferred); or
  • a puzzle url solved up to the point where the puzzle stops being unique; or
  • multiple urls (one per solution)
2025-03-22 Many thanks to PinkHoodie for making the rule panels of spur loop, cover pic and transcribing the original set by Naoki Inaba, and for sending two puzzles (one new, another transcribed) for rollout! 2025-03-22 puzzletters the Two Spur Loop puzzles by David Altizio (djmathman) were added top this page. Thank you! 2025-03-23 puzzletters a 16X6 Spur Loop by PinkHoodie was added - thank you. 2025-04-05 puzzletters PinkHoodie created 1 spur-loop (classic) puzzle - hat tip!