December 1994 - Categories - categories.org.au

question on cHa's
by Thomas Streicher 09 Jan '95

09 Jan '95

Does somebody know whether for a complete Heyting algebra (cHa) A such that the specialization order on points is discrete it automatically holds whether for ALL cHa's B the frame morphisms from A to B are ordered discretely by the spezialization order. I know that there are cases (different from complete Boolean algebras) where it holds but does it hold in general ? Thomas Streicher

2 1

composition of enriched functors
by David Yetter 09 Jan '95

09 Jan '95

It sticks in my mind that somewhere (probably Kelly's book on enriched category theory) I have seen the composition of enriched functors expressed in terms of coends. Our library's copy of Kelly is out, so I was hoping someone could help me recover the result and all necessary hypotheses. More precisely, I recall that it ran like this (and have proved this for ordinary categories): Associate to an enriched functor F:A \rightarrow B the functor Hom(F(-),-):A^{op} \times B \rightarrow V The composition of F and G is then given by \integral^c Hom(F(-),c) \otimes Hom(G(c),-) \cong Hom(G(F(-)),-). I am particularly interested in an analogous result for C-linear categories, and categories enriched in the category of C-linear categories, as this could have applications to topological and conformal field theories. Best Thoughts to all, David Yetter

3 2

G. M. Kelly and anafunctors
by Michael Makkai 16 Dec '94

16 Dec '94

Some weeks ago, Max Kelly brought to my attention his paper "Complete functors in homology I. Chain maps and endomorphisms", Proc. Cambridge Phil. Soc. 60 (1964), pp. 721-735. In section 2, "Generalities on functors", in the first two (full) paragraphs on page 723, he gives a definition of what I call "anafunctor" in my paper "Avoiding the axiom of choice in general category theory" (relatively) recently announced on the Net. He gives both definitions, the elementary one, and the one in the style of spans that I give in my paper. He introduces the concept (that he does not name) as the general form of the data which one is having at one's disposal in many situations when one wants to introduce a functor but the converting of the data into a functor requires a use of the axiom of choice. He does not attempt to develop a theory of such data; however, he does say: "one who will not admit such choices [requiring the axiom of choice] may work with the pair of honest functors S , T [in the span-style definition of "anafunctor"] in place of the dishonest functor ...". Thus, my paper is a working-out of a thirty-year old idea of Max Kelly's. In the paper, I endeavor to show that one can indeed "work with the pair S , T " without giving up the basic structure of category theory. Michael Makkai

1 0

ftp announcement
by Michael Makkai 12 Dec '94

12 Dec '94

Some weeks ago, I announced two papers, "Generalized sketches as a framework for completeness theorems", and "Avoiding the axiom of choice in general category theory" as being available as hard copies. I now have run out of the copies, which were rather expensive because of the lengths of the papers. Now, the same papers have been placed on anonymous ftp at triples.math.mcgill.ca in the directory /pub/makkai ; the first paper is in directory /sketch , the second in /anafun , each paper is in several files. They are also available via WWW ftp://triples.math.mcgill.ca/pub/makkai/makkai_triples.html . If you need help, there is a README file which you can obtain as follows: ftp triples.math.mcgill.ca cd pub/makkai get README bye Michael Makkai

1 0

good times (fwd) last message
by unknown＠categories.mta.ca 08 Dec '94

08 Dec '94

[also noted by Mark Dawson, thanks]

1 0

None
by unknown＠categories.mta.ca 08 Dec '94

08 Dec '94

The last word?: > > U.S. DOE's Computer Incident Advisory Capability > ___ __ __ _ ___ __ __ __ __ __ > / | /_\ / |\ | / \ | |_ /_ > \___ __|__ / \ \___ | \| \__/ | |__ __/ > >Number 94-04 December 6, 1994 > > ------------------- A - T - T - E - N - T - I - O - N ------------------- >| CIAC is available 24-hours a day via its two skypage numbers. To use | >| this service, dial 1-800-759-7243. The PIN numbers are: 8550070 (for | >| the CIAC duty person) and 8550074 (for the CIAC manager). Please keep | >| these numbers handy. | > ------------------------------------------------------------------------- > >Welcome to the fourth issue of CIAC Notes! This is a special edition to >clear up recent reports of a "good times" virus-hoax. Let us know if you >have topics you would like addressed or have feedback on what is useful and >what is not. Please contact the editor, Allan L. Van Lehn, CIAC, >510-422-8193 or send E-mail to ciac(a)llnl.gov. > > $-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$ > $ Reference to any specific commercial product does not necessarily $ > $ constitute or imply its endorsement, recommendation or favoring by $ > $ CIAC, the University of California, or the United States Government.$ > $-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$-$ > >THE "Good Times" VIRUS IS AN URBAN LEGEND > >In the early part of December, CIAC started to receive information requests >about a supposed "virus" which could be contracted via America OnLine, simply >by reading a message. The following is the message that CIAC received: > > --------------------------------------------------------------------------- >| Here is some important information. Beware of a file called Goodtimes. | >| | >| Happy Chanukah everyone, and be careful out there. There is a virus on | >| America Online being sent by E-Mail. If you get anything called "Good | >| Times", DON'T read it or download it. It is a virus that will erase your | >| hard drive. Forward this to all your friends. It may help them a lot. | > --------------------------------------------------------------------------- > >THIS IS A HOAX. Upon investigation, CIAC has determined that this message >originated from both a user of America Online and a student at a university >at approximately the same time, and it was meant to be a hoax. > >CIAC has also seen other variations of this hoax, the main one is that any >electronic mail message with the subject line of "xxx-1" will infect your >computer. > >This rumor has been spreading very widely. This spread is due mainly to the >fact that many people have seen a message with "Good Times" in the header. >They delete the message without reading it, thus believing that they have >saved themselves from being attacked. These first-hand reports give a false >sense of credibility to the alert message. > >There has been one confirmation of a person who received a message with >"xxx-1" in the header, but an empty message body. Then, (in a panic, because >he had heard the alert), he checked his PC for viruses (the first time he >checked his machine in months) and found a pre-existing virus on his machine. > He incorrectly came to the conclusion that the E-mail message gave him the >virus (this particular virus could NOT POSSIBLY have spread via an E-mail >message). This person then spread his alert. > >As of this date, there are no known viruses which can infect merely through >reading a mail message. For a virus to spread some program must be executed. >Reading a mail message does not execute the mail message. Yes, Trojans have >been found as executable attachments to mail messages, the most notorious >being the IBM VM Christmas Card Trojan of 1987, also the TERM MODULE Worm >(reference CIAC Bulletin B-7) and the GAME2 MODULE Worm (CIAC Bulletin B-12). > But this is not the case for this particular "virus" alert. > >If you encounter this message being distributed on any mailing lists, simply >ignore it or send a follow-up message stating that this is a false rumor. > >Karyn Pichnarczyk >CIAC Team >ciac(a)llnl.gov > > >------------------------------ >Contacting CIAC > >If you require additional assistance or wish to report a vulnerability, call >CIAC at 510-422-8193, fax messages to 510-423-8002 or send E-mail to >ciac(a)llnl.gov. For emergencies and off-hour assistance, call 1-800-SKY-PAGE >(759-7243) and enter PIN number 8550070 (primary) or 8550074 (secondary). >The CIAC Duty Officer, a rotating responsibility, carries the primary >skypager. The Project Leader carries the secondary skypager. If you are >unable to contact CIAC via phone, please use the skypage system. > >------------------------------ >This document was prepared as an account of work sponsored by an agency of >the United States Government. Neither the United States Government nor the >University of California nor any of their employees, makes any warranty, >express or implied, or assumes any legal liability or responsibility for the >accuracy, completeness, or usefulness of any information, apparatus, product, >or process disclosed, or represents that its use would not infringe privately >owned rights. Reference herein to any specific commercial products, process, >or service by trade name, trademark, manufacturer, or otherwise, does not >necessarily constitute or imply its endorsement, recommendation or favoring >by the United States Government or the University of California. The views >and opinions of authors expressed herein do not necessarily state or reflect >those of the United States Government or the University of California, and >shall not be used for advertising or product endorsement purposes. > >------------------------------ >End of CIAC Notes Number 94-04 94_12_06 >****************************************

1 0

Re: virus alert (3 posts)
by unknown＠categories.mta.ca 07 Dec '94

07 Dec '94

[note from moderator: the situation is unclear, make of it what you will, but after these 3 posts, discussion of the issue should take place elsewhere. Bob]

1 0

None
by David B. Benson 07 Dec '94

07 Dec '94

I have recently received a message claiming that "good times" is a fake virus alert. Otherwise stated, "good times" is not a virus at all. Under these uncertain circumstances, let the downloader beware.

1 0

None
by Michel Eytan LILoL 07 Dec '94

07 Dec '94

>Date: Wed, 7 Dec 94 09:24:28 EST >From: Michael Barr <barr(a)triples.math.mcgill.ca> > [snip] >- From: CSBN0::CHAU "Elizabeth Chau" 6-DEC-1994 11:32:28.96 >- To: CSBN >- CC: CHAU >- Subj: virus alert >- >- >- Some miscreant is sending e-mail under the title "good times" nation-wide. >- If you get anything like this, DON'T DOWNLOAD THE FILE! It has a virus that >- rewrites your hard drive, obliterating anything on it. >- >- Please be careful and forward this warning to anyone you care about. >- This has turned out to be a *hoax*. Unless you use a mailer like Eudora that launches eg decompacters for attached files, mail cannot contaminate with a virus. -- Michel Eytan, U Strasbourg II eytan(a)dpt-info.u-strasbg.fr "Je dis ce que je pense et je pense ce que je dis"

1 0

None
by RDAWSON＠HUSKY1.STMARYS.CA 07 Dec '94

07 Dec '94

Rumor has it that this "good-times" virus is a text file that can cause damage when read. Don't laugh. It may not be possible on more rationally-designed systems <grin> but on PC's, yes, there is such a thing as a text file that "when you read it you turn intoa toad". Or at least your hard drive does. How such a thing works... the ANSI escape codes are an inter-system set of commands to do things like change text color, font, etc. They are intended to be grabbed by the screen handler and acted on, without actually being passed tothe screen - a little like a tab code or end-of-line code. The ANSI standard ones are all quite harmless, except forthe comparatively harmless practical joke of making background & foreground the same color so you can't read the screen. The DOS handler, ANSI.SYS, however, has a few extras built in. In particular, there is one clever one that remaps the keyboard if you want to. So you can have a French or Dvorak keyboard, for inmstance. But, in a fit of overenthusiasm, they went a bit far, and allowed it to assign a *string* of characters to any key. So you can redefine the [ENTER] key to produce the string "erase *.exe". Or, presumably, to enter a little DEBUG script to create just about any machine-code program you want. Details of this nice little pistol are in all good DOS manuals, even the one you get with DOS ;-) I don't know if this can be done on other machines or not. But it certainly can [it seems] on a PC. So this apparently Dungeons-and-Dragons story should be taken seriously. Yours, Robert

1 0