bugGNU TeXmacs - Bugs: bug #1817, import of \over and \atop

 
 

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bug #1817: import of \over and \atop

Submitted by:  David Allouche <ddaa>
Submitted on:  Wed 27 Nov 2002 07:43:14 PM UTC  
 
Category: ConversionPriority: 5 - Normal
Item Group: ErrorStatus: In Progress
Privacy: PublicAssigned to: Francois Poulain <fpoulain>
Originator Name: Open/Closed: Accepted
Release: 1.0.0.22Release: None
Fixed Release: NoneFixed Release: 
Keywords: tex mathematical math fraction

Tue 31 Jan 2012 11:50:09 AM UTC, comment #1:

The bug has been fixed since 2002, but there also exist other TeX primitives with the same (ugly) behavior :
\above <dimen>
\overwithdelims <delim> <delim>
\atopwithdelims <delim> <delim>
\abovewithdelims <delim> <delim> <dimen>

Those are called "generalized fraction command". Following the TeX book (p292) : «

When TEX sees a generalized fraction command it takes the entire
current list and puts it into the numerator field of a generalized fraction item. The
denominator field of this new item is temporarily empty; the left and right delimiter
fields are set equal to the specified delimiter codes. TEX saves this generalized fraction
item in a special place associated with the current level of math mode processing.
(There should be no other generalized fraction item in that special place, because
constructions like ‘a\over b\over c’ are illegal.) Then TEX makes the current list
empty and continues to process commands in math mode. Later on, when the current
level of math mode is completed (either by coming to a ‘$’ or a ‘}’ or a \right,
depending on the nature of the current group), the current list will be moved into the
denominator field of the generalized fraction item that was saved; then that item, all by
itself, will take the place of the entire list. However, in the special case that the current
list began with \left and will end with \right, the boundary items will be extracted
from the numerator and denominator of the generalized fraction, and the final list will
consist of three items: left boundary, generalized fraction, right boundary.

»

Francois Poulain <fpoulain>
Project MemberIn charge of this item.
Wed 27 Nov 2002 07:43:14 PM UTC, original submission:

> --
> \begin{displaymath}
> {1 \over a-b}
> \end{displaymath}
> --
>
> it gives us a converted result
> 1 1
> --- - b, not -------
> a a - b
>
> The latter is what it means.


Yes, this is a nasty bug, because the parsing of \over (and \atop) is very special; that is probably why these commands are eliminated in LaTeX. We will see if we can do something about it.

David Allouche <ddaa>
Project Administrator

 

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Follow 7 latest changes.

Date Changed By Updated Field Previous Value => Replaced By
Tue 31 Jan 2012 11:50:09 AM UTCfpoulainStatusNone=>In Progress
  Assigned tovdhoeven=>fpoulain
  Summaryimport of \\over and \\atop=>import of \over and \atop
Sun 08 Dec 2002 05:27:50 PM UTCddaaOpen/ClosedOpen=>(Error - Not Found)
  Release1.0.0.22=>(Error - Not Found)
  Release=>
Wed 27 Nov 2002 07:46:54 PM UTCddaaSummaryimport of /over and /atop=>

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