


Addenda to recent articles 200801
Here are some notes on posts from the last
month that I couldn't find better places for.
 As a result of my research into the Harriet Tubman mural that was
demolished in 2002, I learned that it had been repainted last year
at 2950 Germantown Avenue.
 A number of readers, including some honesttoGod Italians, wrote
in with explanations of Boccaccio's term
milliantanove, which was variously translated as
"squillions" and "a thousand hundreds".
The "milli" part suggests a thousand, as I guessed. And "anta" is
the suffix for multiples of ten, found in "quaranta" = "forty", akin
to the "nty" that survives in the word "twenty". And "nove" is
"nine".
So if we wanted to essay a literal translation, we might
try "thousantynine". Cormac
Ó Cuilleanáin's choice of "squillions" looks quite apt.
 My article about clubbing
someone to death with a loaded Uzi neglected an essential
technical point. I repeatedly said that
for my $k (keys %h) {
if ($k eq $j) {
f($h{$k})
}
}
could be replaced with:
f($h{$j})
But this is only true if $j actually appears in %h.
An accurate translation is:
f($h{$j}) if exists $h{$j}
I was, of course, aware of this. I left out discussion of this
because I thought it would obscure my point to put it in, but I was
wrong; the opposite was true.
I think my original point stands regardless,
and I think that even programmers who are unaware of the existence of
exists should feel a sense of unease when presented with (or
after having written) the long version of the code.
An example of this
error appeared on PerlMonks shortly after I wrote the article.
 Robin Houston provides another example of a
nonstandard adjective in mathematics: a quantum group is not
a group.
We then discussed the use of nonstandard adjectives in biology. I
observed that there seemed to be a trend to eliminate them, as with
"jellyfish" becoming "jelly" and "starfish" becoming "sea star". He
pointed out that botanists use a hyphen to distinguish the standard
from the nonstandard: a "white fir" is a fir, but a "Douglasfir" is
not a fir; an "Atlas cedar" is a cedar, but a "western redcedar" is
not a cedar.
Several people wrote to discuss the use of "partial" versus "total",
particularly when one or the other is implicit. Note that a total
order is a special case of a partial order, which is itself a special
case of an "order", but this usage is contrary to the way "partial"
and "total" are used for functions: just "function" means a total
function, not a partial function. And there are clear cases where
"partial" is a standard adjective: partial fractions are fractions,
partial derivatives are derivatives, and partial differential
equations are differential equations.
 Steve Vinoski posted a very interesting solution to my
question about how to set Emacs file modes: he suggested
that I could define a replacement aput function.
 In my utterly useless review of Robert Graves' novel King
Jesus I said "But how many of you have read I,
Claudius and Suetonius? Hands? Anyone? Yeah, I didn't think
so." But then I got email from James Russell, who said he had indeed
read both, and that he knew just what I meant, and, as a
result, was going directly to the library to take out King
Jesus. And he read the article on Planet Haskell. Wow! I am
speechless with delight. Mr. Russell, I love you. From now on,
if anyone asks (as they sometimes do) who my target audience is, I
will say "It is James Russell."
 A number of people wrote in with examples of "theorems" that were
believed proved, and later turned out to be false. I am preparing a
longer article about this for next month. Here are some teasers:
 Cauchy
apparently "proved" that if a sum of continuous functions converges
pointwise, then the sum is also a continuous function, and this error
was widely believed for several years.
 I just learned of a major
screwup by none other than Kurt Gödel concerning the decidability
of a certain class of sentences of firstorder arithmetic which went
undetected for thirty years.
 Robert Tarjan proved in the
1970s that the time complexity of a certain algorithm for the
unionfind problem was slightly worse than linear. And several people
proved that this could not be improved upon. But Hantao Zhang has a paper
submitted to STOC
2008 which, if it survives peer review, shows that that the
analysis is wrong, and the algorithm is actually O(n).
 Finally, several people, including John Von Neumann, proved that the
axioms of arithmetic are consistent. But it was shown later that no
such proof is possible.
 A number of people wrote in with explanations of "more than twenty states"; I
will try to follow up soon.
[Other articles in category /addenda]
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