From: Andreas Strotmann <Strotmann@rrz.Uni-Koeln.DE>

Date: Thu, 25 Sep 1997 20:49:18 +0200

Message-Id: <9709252049.ZM26945@rs3.rrz.Uni-Koeln.DE>

To: www-math@w3.org

Cc: strotmann@rs3.rrz.Uni-Koeln.DE

Date: Thu, 25 Sep 1997 20:49:18 +0200

Message-Id: <9709252049.ZM26945@rs3.rrz.Uni-Koeln.DE>

To: www-math@w3.org

Cc: strotmann@rs3.rrz.Uni-Koeln.DE

Hi, I like the MathML proposal very much. I'm particularly glad to note the clean distinction bteween presentation and content markup observed in the proposal. Th following proposals are concerned only with content markup (excpting the postscriptum which gives a reference to a Unicode font glyph source). I would like to make a point regarding the BVAR element that was discussed at considerable length during the Dublin OpenMath workshop late last year. It was while discussing the representation of an integral that this point came up, so it is in this context that I would like to reiterate the point made there. (Please forgive me if it has been discussed and perhaps dismissed in the WWW-Math group before. I did mention planning to write about this to an active member of the mailing list, and he didn't warn me off.) The MathML draft proposes the following representation for an indefinite integral: <INT> <LOWLIMIT> <MI> 0 </MI> </LOWLIMIT> <UPLIMIT> <MI> y </MI> </UPLIMIT> <EXPR> <MI> x </MI> </EXPR> <BVAR> <MI> x </MI> </BVAR> </INT> Now, consider the (semantic) scope of x and y here. Clearly, the scope of the BVAR x is the <EXPR>...</EXPR> sub-expression, but the LOW/UP-LIMIT sub-expressions are _outside_ its scope. (Try replacing x by y and vice versa, and then imagine an unchanged \forall y surrounding it way up the hierarchy). According to the draft introduction, a guiding principle of the representation chosen for the content markup is that "logical braces" should correspond to sub-expression formation. This principle appears to correspond to the "compositionality principle" of formal semantics in linguistics. I would like to argue, as was successfully argued at the OpenMath meeting mentioned before, that the representation of the integral as proposed in the draft violates the "logical bracing" criterion -- a criterion that I believe to be of fundamental importance for any content markup. More generally, I would like to argue that _scoping_ is a fundamentally important criterion for determining "proper" "logical braces". The MathML draft recognizes this explicitly for operator scoping; I would like to propose that this be recognized as well for variable scoping. In the case of the INT example, the following two possible solutions to this problem come to mind: a) <INT> <EXPR> <MI> x </MI> <BVAR><MI> x </MI></BVAR> </EXPR> <LOWLIMIT> 0 </LOWLIMIT> <UPLIMIT> <MI> x </MI> </UPLIMIT> </INTEGRAL> b) <EXPR> <EXPR> <INT/> <MI>x</MI> <BVAR><MI>x</MI></BVAR> </EXPR> <LOWLIMIT/> 0 <UPLIMIT/> <MI> x </MI> </EXPR> (Similar comments apply, of course, to the SUM and PRODUCT elements, and in "advanced" MathML to a host of other operators.) Solution a) is equivalent to the OpenMath 1.0 solution adopted at the aforementioned meeting, except that BVAR is called LAMBDA there for rather obvious reasons. In solution b), INT becomes a normal operator, as do LOWLIMIT and UPLIMIT, both of which thus become available for arbitrary meaningful combinations. Both solutions share a common fundamental property: A BVAR's logical scope is it's immediately surrounding expression; i.. the scope of the variable(s) listed in the BVAR subexpression is the sub-exprssion immdiately enclosing the BVAR sub-expression. This -- or a similar -- property of the BVAR element I would like to propose to add to the MathML draft for content markup. It is my feeling that it is very important to do so if we're truly talking about "content markup". Historical precedent such as lambda calculus or the constructive proofs of Goedel's theorems show that semantic represenations of maths profit from a syntactic structure that mirrors the semantic structure, and from simple, universal, unequivocal scoping rules for both operators and variables. "Corollaries" A few more suggestions come to mind in this context: * add <VAR> and <CONST> containers, as the distinction between variables, constants, and operators (<FN>) is of fundamental importance. * allow <BVAR> x <SEP/> y </BVAR> * the following is often found in German high school text books, I believe: \forall x\in \R : \sin^2 x + \cos^2 x = 1 Proposal: <EXPR><FORALL/> <BVAR><VAR>x</VAR> <IN/> <CONST><REALS/></CONST></BVAR> <EXPR> ... </EXPR> </EXPR> * allow <BVAR> <MSUB><MI>x</MI> 1</MSUB></BVAR> (subscripted variable) * use BVAR in the markup for <SET> .. <ST/> .. </SET>, <LIMIT>, i.e. everywhere a variable is bound by an operator. Miscellaneous * I'm missing <elements> for named constants: e, pi, i, true, false, and for domains: reals, natural and whole numbers, etc. * symbols commonly used at the high school level in Germany that I missed are those for: function composition, Cartesian product, choose operator, quantifiers * the prime operator (f') might be represented like this: <DIFF> <FN>f</FN></DIFF> * the folowing notation is common, and the concept it represents should be present in MathML: f: R -> R x |--> f(x) := x^2 [In all of these I argue that these are common at the high school level, and certainly in first-semester college maths, in Germany. I thus also propose to eliminate the reference to "American" highschools and replace it with "high schools in most countries".] * And finally, may I suggest that the following be valid MathML: <SEMANTICS> <B>Four colors suffice!</B> <EXPR> <FORALL/> ... </EXPR> </SEMANTICS> Sorry for the long message... Regards, Andreas PS: For chapter 6 of the MathML draft it may be of interest to note that the Unicode server (www.unicode.org) now has a fairly complete repertoire of Unicode glyphs online. Thus, in addition to the Unicode code point it is now possible to include a link to the corresponding glyph on the unicode server. For example, ⋖ (U+22D6) is located at http://www.unicode.org/Unicode.charts/Small.Glyphs/22/U+22D6.gif -- Andreas Strotmann / ~~~~~~ \________________A.Strotmann@Uni-Koeln.DE Universitaet zu Koeln /| University of Cologne \ Regionales Rechenzentrum| Regional Computer Center \ Robert-Koch-Str. 10 /| Tel: +49-221-478-5524 |\ Home: -221-4200663 D-50931 Koeln __|__ FAX: +49-221-478-5590 |__________~~~~~~~~~~~~Received on Thursday, 25 September 1997 14:49:37 UTC

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