The Moser Spindle, Drawn and Coloured

The Prompt

Draw the Moser spindle — the seven-vertex, eleven-edge unit-distance graph — with accurate unit distances. Attempt to colour it with three colours; observe the failure. Then colour it with four. Record the drawing, the failed three-colouring attempt (which edges forced the contradiction), and the successful four-colouring. Reflect on what the spindle reveals about the geometry of the plane.

Completion Criteria

A drawing of the Moser spindle with accurate geometry, a demonstration that three colours fail, a valid four-colouring, and a brief note on what the exercise revealed.

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