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File: PhotocopyAMirror

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My latest posts can be
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Previous blog posts:
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  * SieveOfEratosthenesInPython
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----
Additionally, some earlier writings:
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  * ColinsBlog2010
  * ColinsBlog2009
  * ColinsBlog2008
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  * ColinsBlogBefore2007
********
!!! Photocopy A Mirror - 2015/07/29

Recently on Twitter I asked the question:

* What do you get when you _
    photocopy a mirror?

There are actually (at least) three inter-related questions:

* What do you get?
  * How does the photocopier give you that?
  * Why is that the right thing for it to do?

Several people engaged with the question.  One said "Just try it!" and
that's perfectly reasonable, but it only answers the first of this set
of three. Someone else pointed at an answer
''' <a href="http://www.slate.com/blogs/quora/2015/03/01/what_happens_when_you_copy_or_scan_a_mirror.html">on Quora</a>
that correctly
explained /how/ the result is obtained, even though it claims:

* "To understand why we got the result we did, _
     we first need to look at how a scanner works."

No, that's not the why, that's the /how./  It explains /what/ happens,
but it gives no clue as to /why/ the photocopier is designed to work
like that.

So we are left wondering why.  /Why/ do we get the result we do when we
photocopy a mirror?  Can you deduce, purely from what a photocopier does,
what the result /should/ be when you photocopier a mirror?

To quote
''' <a href="https://en.wikipedia.org/wiki/Julius_Sumner_Miller">Julius Sumner Miller</a>:
''' <ul><li><a href="http://www.abc.net.au/science/features/whyisitso/">Why is it so?</a></li></ul>

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