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From: msb@sq.com (Mark Brader)
Newsgroups: comp.dcom.telecom
Subject: Re: Manhole Covers
Message-ID: <59794@bu.edu.bu.edu>
Date: 28 Jun 90 09:25:42 GMT
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X-Telecom-Digest: Volume 10, Issue 460, Message 3 of 11


>>I think this has been discussed before.  Round covers are popular
>>because it's impossible for the cover to fall into the hole.
>This also holds for triangular covers.  (only if they are equilateral,
>though.)

Hold the lid with one edge vertical, and it will go in just fine if
placed next to one edge of the opening.  So an equilateral triangle
*doesn't* work.  What does work is a "Reuleaux triangle", where each
side is not a straight line but an arc centered on the opposite
vertex.  This is the second-simplest (after the circle) of what are
called "curves of constant breadth", any of which will also work.

However, round covers have the additional advantage that there is no
wrong way to put them in the hole.


Mark Brader		  
SoftQuad Inc., Toronto	  
utzoo!sq!msb, msb@sq.com	

P A T R I C K   A.  T O W N S O N  (The Cheerful Iconclast)
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