# Marbles

## Rules[edit]

Find the shading of marbles falling through a grid.

All marbles fall down vertically, one in each column. If a marble hits a diagonal wall, it rotates 90°, moves to the adjacent column and continues falling down vertically there. All marbles fall at the same time, however they do not interact with each other. The grid and the walls are given, no walls can be added or moved.

Each marble consists of four sectors. Each marble is either completely unshaded, or two adjacent sectors are shaded. The numbers outside the grid represent observers; they indicate the total number of shaded sectors of all falling marbles in the upper or lower half of the respective row. In rows with diagonal walls, shaded sectors are counted after the marbles have rotated.

(Rules and example from WPC 2019 IB)

## History of the puzzle[edit]

Appeared on WPC 2019/Round 12, an "innovations" round. The puzzles were written by Roland Voigt.

## Appearances in the past WPCs[edit]

- WPC 2019/Round 12 by Roland Voigt