Yesterday's post, as someone noticed in the discussion chat (Maths Visuals Discussions
https://hottg.com/mathvisuals_chat), was a trick, not a regular polygon construction with rule and compass exactly but a very close approximation.
As 7 is a Pierpont prime but not a Fermat prime, the regular heptagon is not constructible with compass and straightedge but is constructible with a marked ruler and compass. It is the smallest regular polygon with this property. This type of construction is called a neusis construction. It is also constructible with compass, straightedge and angle trisector.
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