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Note on Euclid's elements

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Inspired by Einstein's quote, "If Euclid failed to kindle your youthful enthusiasm, then you were not born to be a scientific thinker," I recently purchased the book "Euclid's Elements" for my son. With this esteemed work on our bookshelf, I hope it brings an opportunity for my children to one day open its pages and delve into a new world of wonder. This post is to share two interesting discoveries after I read the first three pages of the book. Euclid's fourth postulate At the beginning of the book, Euclid proposes five postulates for plane geometry, which I quote directly from this web : A straight line segment may be drawn from any given point to any other.  A straight line may be extended to any finite length.  A circle may be described with any given point as its center and any distance as its radius.  All right angles are congruent.  If a straight line intersects two other straight lines, and so makes the two interior angles on one side of it toget