URN · 16-Triangle Movement Lab

Tap a highlighted tile to reflect it across the shared edge into the blank. Each reflection flips the tile to its opposite face. This prototype tests geometry and movement, not the final number-placement rules.

Four equal subdivisions per side form 16 equilateral cells. The initial blank is an interior triangle. A shuffle uses valid reflections only. Tiles have a distinct front (F) and back (B); their face is tracked by actual movement, not chosen independently. Lettering turns with each tile through every edge flip; back-face lettering remains readable. Use Undo to inspect individual transitions.