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Timeline for Arcular triangle inequality

Current License: CC BY-SA 4.0

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Oct 18, 2023 at 15:12 comment added domotorp Indeed, thank you! Let me confess something. I knew a proof for the case when the arcs bend as in your solution, but it was a tedious computation, see page 17 here: doi.org/10.1007/BF02187821 Your solution is much nicer.
Oct 18, 2023 at 15:09 vote accept domotorp
Oct 18, 2023 at 14:41 history edited Anton Petrunin CC BY-SA 4.0
added 86 characters in body
Oct 18, 2023 at 14:38 comment added Anton Petrunin @domotorp I will fix it, thank you. If arcs can bend the other way, then the statement does not hold. Take $c$ on the arc $ab$ closer to $a$; choose arcs $ac$ that are tangent to the line segment $ab$ and let $bc$ be subarc of $ab$.
Oct 18, 2023 at 14:24 history edited Anton Petrunin CC BY-SA 4.0
added 54 characters in body
Oct 18, 2023 at 8:14 comment added domotorp I assume you mean that first you assume that the arcs are tangent, then claim that equality holds if $c\in [a,b]$. Does your solution also work if one or both of the arcs $ac$ and $cb$ bend the other way?
Oct 18, 2023 at 4:58 history answered Anton Petrunin CC BY-SA 4.0