[next] [prev] [up] Date: Wed, 05 Jan 94 23:34:58 -0500 (EST)
[next] [prev] [up] From: Jerry Bryan <BRYAN%WVNVM.BITNET@mitvma.mit.edu >
~~~ ~~~ [up] Subject: Square Brackets

This posting has very little to do with cubes of any sort, but I
think you may find it of interest anyway. If not, you can just
delete it.

In his analysis of my operator which combines M-conjugation with
a whole cube rotation, Dan Hoey inserted square brackets to make
his exposition more readable. And therein lies a story.

As it turns out, I had composed most of my original note at work,
and I had used square brackets. Actually, I had used square
brackets to delimit the indexes for the rotation and reflection
operations, and I had used parenthesis to delimit the indexes for
the individual cells in the row vectors. I wanted to make a
distinction between the two kinds of indexing. Dan avoids the
necessity for a distinction by simply not detailing the
indexing of the individual cells.

Anyway, I completed the note at home. Much to my dismay, all of my
square brackets had disappeared! I pretty much understand the
problem. My E-mail system is an IBM mainframe which uses EBCDIC as
its basic code. EBCDIC does not deal very well with square brackets.
There are at least two "standards" for encoding square brackets in

There are any number of ways to access an IBM mainframe, but the
native terminal support is 3270 terminals using EBCDIC. Both at home
and at work, I use a PC running TN3270 to access our mainframe.
TN3270 is a 3270 version of TELNET. However, the TN3270 I use at work
is considerably different from the TN3270 I use at home. One TN3270
implements one of the square bracket standards, and the other
TN3270 implements the other.

For similar reasons, mail gateways often have difficulties with
square brackets. They may have to translate EBCDIC to ASCII or
ASCII to EBCDIC, and it is difficult to know how best to set up
the translate tables. My experience is that some gateways get it
"right" and others get it "wrong". I therefore had a great fear
that if I posted my note with square brackets, that the square brackets
might appear as gibberish to at least some of you. Thus, I sort
of temporized and faked the subscripts with upper and lower
case letters (e.g., Bk to mean B-sub-k), omitting square brackets

It is probably no accident that old programming languages such
as FORTRAN and COBOL use parentheses for indexing. These languages
originated in the 50's. At that time, the dominant character
code was BCD, which did not include square brackets. EBCDIC is just
extended BCD, and the original EBCDIC did not include square brackets,
either. Square brackets are a latter day addition to EBCDIC, and
the implementation of square brackets in EBCDIC is inconsistent.

ASCII has always included square brackets. "Modern" languages
(say, starting in the 70's) such as Pascal and C (and their
descendents) grew up in the ASCII world, and tend to use
square brackets for indexing and parentheses for function
arguments. FORTRAN compilers to this day have difficulty figuring
out with things like Y=X(I) or Y=F(X) -- which are functions and
which are subscripted arrays. Also, Pascal and C tend not to
co-exist very well in the EBCDIC world because of these kinds of
character set difficulties.

There are several other characters with similar difficulties. For
example, if G is the cube group, you might want to refer to the
size of the cube group as |G|. But the delimiting vertical bars
can be very different between EBCDIC and ASCII. Finally, FORTRAN
used ** for exponentiation. More modern languages tend to use
some sort of up-arrow or carat. But such characters don't
translate well between EBCDIC and ASCII. For example, if I
write |G| = 4.3 * 10^19, it is highly problematic whether the
character between the 10 and the 19 which I am using to express
exponentiation will make any sense on your particular system.

For whatever it is worth, here are my home and work versions of
square brackets:

home left  square bracket  [[[[[[[ x'AD'
home right square bracket  ]]]]]]] x'BD'
work left  square bracket   x'BA'
work right square bracket   x'BB'

 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Robert G. Bryan (Jerry Bryan)              (304) 293-5192
Associate Director, WVNET                  (304) 293-5540 fax
837 Chestnut Ridge Road                     BRYAN@WVNVM
Morgantown, WV 26505                        BRYAN@WVNVM.WVNET.EDU

If you don't have time to do it right today, what makes you think you are
going to have time to do it over again tomorrow?

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