First, let me say that I hadn't expected an idle musing to prompt what's become the most active comment thread so far on an otherwise obscure and rarely updated blog. In defense of VHEMT, I'd like to point out that it's a fairly benign form of a rather sinister movement. As Exhibit 1, below I'll post in full the comments of Anonymous (due the the length, the really juicy parts were clipped from the comment text). Imprisonment, forced sterilization -- it's all in there, enjoy. For Exhibit 2, consider Pollute and Die clip released by the 1010 campaign. They seem to have crossed a line here -- "snarling, wicked, homicidal misanthropy" is a fair characterization of this stunt. The reaction was one of such unanimous disgust that these people were compelled to issue a (weak) retraction.

These people are too easily dismissed as inconsequential raving lunatics. Occasionally, we're rudely reminded that all this talk of mass-murder isn't mere talk.

------------------- Anonymous's comment -------------------

sorry, i posted it to another forum of similar title...anyway if you want something to knaw on give it a thorough read...

***The Global Non-transferable 0.5 limit plan***

The basis of the argument...

1) we are approximately 50% over global carrying capacity as a species.

2) one child can carry the biological records for two...where a second child assumes the burden of the necessary reduction in population be an involuntary forfeiture of the biological records of two other individuals...

3) under awareness of said earth system stress levels, and loss of specification, many may voluntarily forfeit the passing of their biology as a means of preserving species on the brink, and securing planetary health, while insuring the right of humans to breed, should they choose to, remain an accessible option....in order that this wish be respected, these voluntary forfeitures must not be allowed to become a birth credit to be assumed by any existing parent, maternal, paternal, or both, in the case of a second potential child.

In order that human rights be observed:

The following proposal sites the rights of children not yet created as per 1) that they may not be born into a world that cannot adequately support them, or if this world can arguably support them, that one may site a degraded world relative to that which the potential child’s forbears enjoyed would be the child’s inheritance…

The following proposal sites the right of humans to procreate as per 2), while imposing limits to protect the rights of others who may choose to employ this right…

The following proposal sites the right to chose not to reproduce, as per 3)

Proposed proceedings to safe guard these rights are as follows, and are to be applied equally on a global scale to all members of the human populous.

Initial Proceedings:

all male parents of existing children, that are not already fixed, would need to schedule an appointment to address the situation, or face issuance of a warrant for their arrest for obstruction of justice and associated fines....

all female parents of two or more existing children that are not fixed, would need to schedule an appointment to address the situation, or face issuance of a warrant for their arrest for obstruction of justice and associated fines....

all female parents of fewer than two existing children, should be informed that weather though abstinence, birth control, selection of a fixed male partner, or any other means, they may wish to avoid fines and procedures.

Protocol:

Post conception the suspected father would be incarcerated until such a

time that it can be determined beyond question that he indeed is the

father...If he is not the father; he is free to go... The woman

then would be incarcerated until such a time as she could provide sufficient information to bring the father of her child into custody. Upon determination, the father of the child would undergo vasectomy before being released...

Should the mother choose to terminate the pregnancy in the first trimester, the father would be released unaltered. If the mother does not choose to terminate the pregnancy within the first trimester, this becomes a default decision to carry the child to term under the fore mentioned proceedings.

In any cases of a potential child, by a parent of an existing child, paternal, maternal or both, the offender(s) would have the choice of aborting the child or being put to death. The former decision inclusive of fines: for a father potentially twice ,for assuming what should rightfully be the woman's choice, and for a mother potentially twice, as a means of securing finance for the tubal she would receive in post.

Should any geographical region reach a state of equilibrium within it’s boundaries, the populous will have the option of applying for revokeable immunity.

## Saturday, October 2, 2010

## Monday, September 13, 2010

### The Voluntary Human Extinction Movement

Have you heard of The Voluntary Human Extinction Movement? Their basic premise is that we should save the earth by not having any more children. I'm still not 100% sure this isn't a joke, but if it is, it's definitely on the elaborate side. What with the website translated into 17 languages, plus films and comics -- it's hard not to come to the conclusion that, at the very least, these guys take themselves seriously.

And yet the lack of self-awareness is surreal, bordering on (and occasionally crossing into) the comical. Consider their Why Breed chart (scroll down). It starts with the premise that "the search for a rational, ethical reason for creating one more human today goes on without success" and proceeds to list the various pretexts people give for having children, expose the true motivation behind each one, and offer helpful alternatives -- all in a convenient three-column format.

Some of these are jaw-droppingly idiotic (pretext: "Pregnancy and childbirth are life experiences"; suggestion: "Rent pregnancy simulator". Huh? Is that a meta-joke?). Others are dutifully cribbed from the multikulti book (pretext: "Want a child with our bloodline"; true motivation: "Ego extension. Racial identity"; suggestion: "Recognize value of people with different genetic makeups").

But this one is telling: "God wants us to." One might naively assume that the VHEMTers are hard-core atheists, but a moment's reflection suggests that this can't be the case. Why would a true atheist give a rat's behind about the future of the earth, after his own death? Make no mistake, this is a religious cult. Unsurprisingly, the VHEMTer rebuttal to G-d's commandment is a direct call to convert: "Seek true nature of God, whatever you perceive God to be." They don't say this directly, but Wiccanism seems to capture their creed best: "Stop. Having. Babies."

I have no interest in dialogue with these people (I shouldn't even be taking the time to blog about them). But I am mighty curious to know how they'd respond to my silver-bullet argument:

There are two kinds of people in this world: those who will sign on to the VHEMT agenda and those who will not. Which group does the future belong to? What does this say about the effectiveness of the VHEMT agenda?

And yet the lack of self-awareness is surreal, bordering on (and occasionally crossing into) the comical. Consider their Why Breed chart (scroll down). It starts with the premise that "the search for a rational, ethical reason for creating one more human today goes on without success" and proceeds to list the various pretexts people give for having children, expose the true motivation behind each one, and offer helpful alternatives -- all in a convenient three-column format.

Some of these are jaw-droppingly idiotic (pretext: "Pregnancy and childbirth are life experiences"; suggestion: "Rent pregnancy simulator". Huh? Is that a meta-joke?). Others are dutifully cribbed from the multikulti book (pretext: "Want a child with our bloodline"; true motivation: "Ego extension. Racial identity"; suggestion: "Recognize value of people with different genetic makeups").

But this one is telling: "God wants us to." One might naively assume that the VHEMTers are hard-core atheists, but a moment's reflection suggests that this can't be the case. Why would a true atheist give a rat's behind about the future of the earth, after his own death? Make no mistake, this is a religious cult. Unsurprisingly, the VHEMTer rebuttal to G-d's commandment is a direct call to convert: "Seek true nature of God, whatever you perceive God to be." They don't say this directly, but Wiccanism seems to capture their creed best: "Stop. Having. Babies."

I have no interest in dialogue with these people (I shouldn't even be taking the time to blog about them). But I am mighty curious to know how they'd respond to my silver-bullet argument:

There are two kinds of people in this world: those who will sign on to the VHEMT agenda and those who will not. Which group does the future belong to? What does this say about the effectiveness of the VHEMT agenda?

## Wednesday, July 7, 2010

### Smart spam?

Occasionally I'll get comments that are clearly spam (since this blog is rarely updated, feel free to replace "occasionally" with "rarely"). Ordinarily, I delete them without a second thought. Two recent comments, however, gave me reason for pause.

I am talking about this and this. These comments are a bit of a mystery to me. First, note that they are not only syntactically but also

Explanations welcome...

I am talking about this and this. These comments are a bit of a mystery to me. First, note that they are not only syntactically but also

*semantically*more or less well-formed. They are even vaguely relevant to the post's content! So a natural hypothesis might be that they were written by humans. But then why the obviously spammy aliae (aliases) --- "buy sildenafil citrate" and "generic viagra"?Explanations welcome...

## Wednesday, January 13, 2010

### Ode to my students + moralizing

First, two tales of hubris and folly. The recursion theorem was a big success with my students. We don't usually teach it in this course, but my students went through the standard material like pie and were hungry for more. Other than a ridiculously easy proof of the undecidability of the halting problem, the recursion theorem yields a slick proof that L_min is not in RE (good luck approaching that one without this tool). Riding a euphoric wave of success, I thought I'd improvise a proof that L_min is not in coRE. I thought I had a clever proof using the fixed-point theorem, but it turned out to be wrong. After spending a couple of days in search of a proof, I turned to mathoverflow (an amazing resource!) where Ryan Williams produced a correct proof.

Second, during the last lecture, a student asked if every undecidable language in RE is complete for RE under mapping reductions. I thought the answer should be true, and tried to prove this during the break. Needless to say, I failed to find a proof. After speaking with Menachem Kojman, I learned that in fact the answer is false; this follows froom the Friedberg-Muchnik theorem.

There are two morals to this story:

1. I was blessed with amazing students this semster.

2. Sometimes (if one is lucky!) innocent-sounding questions that come up in undergraduate lectures turn out to be deep, difficult research problems. By all means attempt to tackle them, but keep in mind this caveat.

Second, during the last lecture, a student asked if every undecidable language in RE is complete for RE under mapping reductions. I thought the answer should be true, and tried to prove this during the break. Needless to say, I failed to find a proof. After speaking with Menachem Kojman, I learned that in fact the answer is false; this follows froom the Friedberg-Muchnik theorem.

There are two morals to this story:

1. I was blessed with amazing students this semster.

2. Sometimes (if one is lucky!) innocent-sounding questions that come up in undergraduate lectures turn out to be deep, difficult research problems. By all means attempt to tackle them, but keep in mind this caveat.

## Saturday, January 9, 2010

### Show that L_min is not in coRE

So I taught the recursion theorem and showed (as in Sipser) that the language L_min, consting of all minimal Turing machine descriptions, is not recursively enumerable (RE). The argument goes like this: suppose to the contrary that L_min is in RE, with some enumerator E. Define the Turing machine B, which obtains its own description [B] via the recursion theorem, waits until E generates a program C that is longer than [B], and then simulates the behavior of C. The contradiction results from the assumption that E only generates minimal programs and the construction of B as a program that's shorter than some "minimal" program!

Now I want to show that L_min is not in coRE (meaning that its complement is not in RE). This has turned out to be quite a bit trickier, at least for me! I believe I have a proof, but I welcome solutions from the readers.

Now I want to show that L_min is not in coRE (meaning that its complement is not in RE). This has turned out to be quite a bit trickier, at least for me! I believe I have a proof, but I welcome solutions from the readers.

## Saturday, January 2, 2010

### A cheating Quine?

So I'm teaching a course on automata theory -- again. (A brief personal update: I've started a faculty position at BGU, got married and had a baby -- not in that order.)

I want to teach the recursion theorem this week. The theorem states that no matter what Turing machine one is designing, one can always assume that it has access to its own description.

To me, this always seemed painfully obvious. Once you accept that Turing machines and programs (in MATLAB, say -- to be concrete) are equivalent, the argument comes down to writing a program that can print its own code.

At first, writing a program that prints itself might seem impossible. After all, any sort of program that says PRINT X will be longer than the string X (because it contains X and the PRINT instruction) -- and so X can't be the program's whole description!

Indeed, such a simple strategy for a self-printing program is doomed to failure. However, who says the program must quote itself within itself verbatim? Maybe it can encode a description of itself in some compressed form, and execute a routine that decompresses and prints that description. Indeed, many such programs exist -- they are known as quines (after the great logician and philosopher Quine).

But it seems to me that these quines, while clever, are working too hard. Consider the following simple MATLAB function:

function quinecheat

fid = fopen('quinecheat.m','r');

str = char(fread(fid))';

% remove double line-skips:

str = strrep(str,[char(13) char(10)],char(10));

fclose(fid);

fprintf('%s\n',str);

return

If you save the code above as the MATLAB file 'quinecheat.m' and call quinecheat from the MATLAB command window, you will get a printout of the code.

On the one hand, you can do this in just about any programming language -- and any Turing machine T can assume it's being simulated on some universal Turing machine U and move U's tape head to the beginning of T's description. Also, I believe that this trivial "proof" of the recursion theorem retains the theorem's full power. For example, here is a simple proof that the halting problem is undecidable. Suppose to the contrary that some matlab function H inputs other matlab programs and outputs 1 if the input program halts (and 0 otherwise). Now consider the matlab function D which obtains its own description [D] and calls H([D]). If H([D])=1, D goes into an infinite loop; otherwise, D halts. We've reached our contradiction!

And yet I can't help but feel that I'm cheating somewhere. Is my program quinecheat a valid example of a self-printing program? Is the technique I am suggesting a valid alternative proof of the recursion theorem?

I want to teach the recursion theorem this week. The theorem states that no matter what Turing machine one is designing, one can always assume that it has access to its own description.

To me, this always seemed painfully obvious. Once you accept that Turing machines and programs (in MATLAB, say -- to be concrete) are equivalent, the argument comes down to writing a program that can print its own code.

At first, writing a program that prints itself might seem impossible. After all, any sort of program that says PRINT X will be longer than the string X (because it contains X and the PRINT instruction) -- and so X can't be the program's whole description!

Indeed, such a simple strategy for a self-printing program is doomed to failure. However, who says the program must quote itself within itself verbatim? Maybe it can encode a description of itself in some compressed form, and execute a routine that decompresses and prints that description. Indeed, many such programs exist -- they are known as quines (after the great logician and philosopher Quine).

But it seems to me that these quines, while clever, are working too hard. Consider the following simple MATLAB function:

function quinecheat

fid = fopen('quinecheat.m','r');

str = char(fread(fid))';

% remove double line-skips:

str = strrep(str,[char(13) char(10)],char(10));

fclose(fid);

fprintf('%s\n',str);

return

If you save the code above as the MATLAB file 'quinecheat.m' and call quinecheat from the MATLAB command window, you will get a printout of the code.

On the one hand, you can do this in just about any programming language -- and any Turing machine T can assume it's being simulated on some universal Turing machine U and move U's tape head to the beginning of T's description. Also, I believe that this trivial "proof" of the recursion theorem retains the theorem's full power. For example, here is a simple proof that the halting problem is undecidable. Suppose to the contrary that some matlab function H inputs other matlab programs and outputs 1 if the input program halts (and 0 otherwise). Now consider the matlab function D which obtains its own description [D] and calls H([D]). If H([D])=1, D goes into an infinite loop; otherwise, D halts. We've reached our contradiction!

And yet I can't help but feel that I'm cheating somewhere. Is my program quinecheat a valid example of a self-printing program? Is the technique I am suggesting a valid alternative proof of the recursion theorem?

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