<br><br><div class="gmail_quote">2009/12/9 Richard O'Keefe <span dir="ltr"><<a href="mailto:ok@cs.otago.ac.nz">ok@cs.otago.ac.nz</a>></span><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div class="im"><br>
On Dec 10, 2009, at 2:58 AM, Roel van Dijk wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
I tried to be conservative with the choice of unicode symbols. I have<br>
defined the division sign (÷) to be (/). But it could just as well be<br>
defined as 'div'.<br>
</blockquote>
<br></div>
No it couldn't. One expects 3÷2 to be 1½, not 1.<br>
You will, for example, find this text on the web:<br>
"Mathematically, the division sign is equivalent to the forward slash.<br>
Thus, for example, 4 ÷ 5 = 4/5 = 0.8"<br>
This is actually historically backwards. When I was a nipper,<br>
1/6 meant "one and six" or "eighteen pence" or at least three<br>
loaves of good bread. As far as I'm aware, the use of "/"<br>
instead of "÷" is a computerism introduced in the days of 6 bit<br>
character sets.<div class="im"><br>
<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Another choice that could lead to some discussion is the definition of<br>
(⊂) to be 'Data.Set.isProperSubsetOf' and (⊆) to be<br>
'Data.Set.isSubsetOf'. An alternative choice would be to have (⊊) for<br>
'isProperSubsetOf' and (⊂) for 'isSubsetOf'.<br>
</blockquote>
<br></div>
Mathematicians may use the plain horseshoe for either subset or<br>
proper subset, depending on the author. But I've never ever seen<br>
anyone use the horseshoe with an equals bar for proper subset;<br>
that would really make no sense.<br></blockquote><div><br>The second notation uses a horseshoe with an equals bar and a _slash_ through it to indicate proper subset, and I have seen that several times before; however, I prefer the first notation style.<br>
</div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br>
I suggest that you take the Z formal specification language as your<br>
guide (plain horseshoe is proper subset, horseshoe with equal bar is<br>
subset-or-equal). If you don't like Z, try B: same thing.<div><div></div><div class="h5"><br>
<br>
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</div></div></blockquote></div><br><br clear="all"><br>-- <br>James Hall<br>