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We want to join by a line two distinct points $A$ and $B$. We have only a ruler of length $l>0$ and a pen. If $AB>l$ how can we do this? Imagine a method that works when $AB$ is really huge and we cannot draw a line close to $B$.

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    $\begingroup$ It can be done using the Desargues theorem. Is the reason of the downvotes the fact that it is not exactly research level? $\endgroup$ Commented Nov 30, 2014 at 19:53
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    $\begingroup$ @DanielSoltész I've also posted the question on stackexchange but I am not satisfied with the solution posted there. I hope you can give me some advice. Thanks a lot! Here it is math.stackexchange.com/questions/1042541/how-can-we-draw-a-line $\endgroup$
    – Bogdan
    Commented Nov 30, 2014 at 22:00
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    $\begingroup$ @Bogdan: You might have mentioned sooner that the question had already been posted on math.SE. $\endgroup$ Commented Nov 30, 2014 at 22:10
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    $\begingroup$ @Bogdan, why are you not satisfied with that solution? It seems fine to me. $\endgroup$ Commented Dec 1, 2014 at 3:27
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    $\begingroup$ This question appears to be a cross-post of an answered question (answerer on math.SE is responsive too). $\endgroup$
    – user9072
    Commented Dec 1, 2014 at 13:46

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