2009/12/9 Richard O'Keefe <o...@cs.otago.ac.nz> > > On Dec 10, 2009, at 2:58 AM, Roel van Dijk wrote: > >> I tried to be conservative with the choice of unicode symbols. I have >> defined the division sign (÷) to be (/). But it could just as well be >> defined as 'div'. >> > > No it couldn't. One expects 3÷2 to be 1½, not 1. > You will, for example, find this text on the web: > "Mathematically, the division sign is equivalent to the forward slash. > Thus, for example, 4 ÷ 5 = 4/5 = 0.8" > This is actually historically backwards. When I was a nipper, > 1/6 meant "one and six" or "eighteen pence" or at least three > loaves of good bread. As far as I'm aware, the use of "/" > instead of "÷" is a computerism introduced in the days of 6 bit > character sets. > > > Another choice that could lead to some discussion is the definition of >> (⊂) to be 'Data.Set.isProperSubsetOf' and (⊆) to be >> 'Data.Set.isSubsetOf'. An alternative choice would be to have (⊊) for >> 'isProperSubsetOf' and (⊂) for 'isSubsetOf'. >> > > Mathematicians may use the plain horseshoe for either subset or > proper subset, depending on the author. But I've never ever seen > anyone use the horseshoe with an equals bar for proper subset; > that would really make no sense. >
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. > > I suggest that you take the Z formal specification language as your > guide (plain horseshoe is proper subset, horseshoe with equal bar is > subset-or-equal). If you don't like Z, try B: same thing. > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- James Hall
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