Triangle billiards
This demo lives at
http://faec.me/files/billiards.html.
Its abstract lives at
http://faec.me/files/billiards.pdf.
Its slides are at
http://faec.me/files/billiards-crm.pdf.
Use WASD / arrows to move the path. Hold shift to move slower. Hold
ctrl-shift to move much slower.
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Do not press