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The example comes from the paper “Transitive sets and cyclic quadrilaterals” by I. Leader,P.A. Russell and Mark Walters. It is here. In corollary 2 of the paper they prove the set $$((-1,0),(1,0),(a,\sqrt{1-a^2},(a,-\sqrt{1-a^2}))$$ where $a$ is transcendental does not embed into any transitive set. This type of set is called a kite.

If you could find a set which satisfies the above properties and prove it is Ramsey that would provide a counterexample to the hypothesis of the first paragraph. In any case this is a good example of a set which is spherical and can’t be embedded into a transitive set. I may continue this series of posts later.

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It finds an example of size 1160 that has value 2 and proves that that example is maximal. The polymath 5 project found an example of size 1124. The proof that 1160 is maximal required a large computer proof. For more information see this post.

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