2009/12/10 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.
Ok, this makes me happy I choose (/) instead of 'div'. >> 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. As James Hall pointed out there is actually a tiny slash trough the equal bar underneath the horseshoe. The fact that this is hard to see is another reason why I choose the first option. > 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. Yes, this is how I have defined things in the current version. Thank you for your comments, Roel _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
