From: mouse@thunder.mcrcim.mcgill.edu (der Mouse)
Subject: rec.puzzles FAQ comments [POSSIBLE SPOILERS]
Organization: McGill Research Centre for Intelligent Machines
Date: Sun, 15 Nov 92 19:23:45 GMT

I read through the whole FAQ list and came up with a few points. I sent
one of these (the first one listed, I think) to the FAQ maintainer, but
there are enough of these that a posting seems warranted, and some of
them could perhaps benefit from other opinions.

> ==> arithmetic/digits/zeros/factorial.p <==
> How many zeros are in the decimal expansion of n!?
> ==> arithmetic/digits/zeros/factorial.s <==

The answer given actually answers the question "How many zeros *end*
the decimal expansion of n!?", not the question asked.

> ==> combinatorics/grid.dissection.p <==
> How many (possibly overlapping) squares are in an mxn grid?
> ==> combinatorics/grid.dissection.s <==

The question is unclear.  Does it mean an rectangle cut up into mxn
squares, from which squares are to be picked out?  Does it mean an mxn
array of points, from which are to be chosen sets of four points that
mark the corners of a square?  Something else?

At any rate, the answer given assumes all the squares are aligned with
their edges parallel to the edges of the mxn grid.  This corresponds to
my first interpretation above.  The second one is much the harder (and
more interesting) problem....

> ==> english/homographs.p <==
> List all homographs (words that are spelled the same but pronounced
> differently)
> ==> english/homographs.s <==

I take exception to three of the answers given:

> A	commune {take Communion; administrative district}
> B	mouse {rodent; to hunt them}
> A	present {current; Christmas ~}

I maintain that:

- "commune" should be classed as B, because I think both meanings are
  related to the root from which we get "community".  (This would
  benefit from attention from an etymologist who knows the words.  I
  could well be wrong.)
- "mouse" should be BE: I and many others I know pronounce both
  meanings identically.
- "present" should be E: ditto.  (The verb meaning I do accent
  differently, but the adjective and noun I pronounce identically.)

> ==> geometry/construction/square.with.compass.p <==
> Construct a square with only a compass and a straight edge.
> ==> geometry/construction/square.with.compass.s <==

The listed construction is unnecessarily complicated.

> Draw a circle (C1 at P1).  Now draw a diameter D1 (intersects at P2
> and P3).  [...] draw a line (D2).  This line should go the center of
> circle C1 at a rt angle to the original diameter line.  This line
> should cross circle C1 at P4 and P5 [...]

The construction goes on.  But at this point, P2, P4, P3, and P5
already form a square; there is no need to mess around more.  (Note
that the question merely asked for a square, not for a square with a
given line segment as one edge.)

> ==> geometry/hole.in.sphere.p <==

The listed solution is all very well, except for possible arguments
about what "length" means when applied to a hole that is of length L
once constructed but involves the removal of material over a length far
greater than L.

However, there is a much shorter answer, based on the assumption that
the problem can be solved: simply note that if the problem can in fact
be solved, then the solution where the sphere is six inches across and
the hole is of zero width provides an immediate answer.

> ==> group/group.02.p <==
> ABEHIKMNOPTXZ CDFGJLQRSUVWY
> ==> group/group.02.s <==
> ABEHIKMNOPTXZ	resembles Greek letter
> CDFGJLQRSUVWY	does not resemble Greek letter

F is an almost perfect digamma, and Q in many fonts is substantially
like a qoppa.  (Neither digamma nor qoppa is used any longer, but there
was a time when they were.)

And whether archaic Greek letters are permitted or not, Y is a great
deal like a capital upsilon.

> ==> group/group.04.p <==
> BDO P ACGJLMNQRSUVWZ EFTY HIKX
> ==> group/group.04.s <==
> BDO		no endpoint
> P		one endpoint
> ACGJLMNQRSUVWZ	two endpoints
> EFTY		three endpoints
> HIKX		four endpoints

If I has four endpoints, serifs must be included, in which case many of
the other answers are wrong: B and D have two, P has three, A four, G
three, etc.

> ==> group/group.05.p <==
> CEFGHIJKLMNSTUVWXYZ ADOPQR B
> ==> group/group.05.s <==
> CEFGHIJKLMNSTUVWXYZ	no enclosed area
> ADOPQR			one enclosed area
> B			two enclosed areas

In fonts with a swash tail for Q, it often encloses two areas.

> ==> induction/paradox.p <==
> What simple property holds for the first 10,000 integers, then fails?
> ==> induction/paradox.s <==

The solution given involves a recusive equality of four terms.  Far
simpler than this, in my opinion, is the property of being no greater
than 10000.  (Duh!)

> ==> logic/riddle.s <==

This one is listed with "???" for the solution...

> Sir, I bear a rhyme excelling
  3  . 1 4    1  5    9
> In mystic force and magic spelling
  2  6      5     3   5     8
> Celestial sprites elucidate
  9         7       9
> All my own striving can't relate
  3   2  3   8        4     6

The apostrophe in "can't" is perhaps a minor flaw, but tolerable.

> ==> logic/timezone.p <==
> Two people are talking long distance on the phone; one is in an
> East-Coast state, the other is in a West-Coast state.  The first asks
> the other "What time is it?", hears the answer, and says, "That's
> funny.  It's the same time here!"
> ==> logic/timezone.s <==

In the situation puzzles outtakes list, we find this same question,
with the listed answer, and also the following:

> 2.15a.  Variant answer: The east-coast state is in the USA, on
> Eastern Daylight time.  The west-coast state is Western Australia.
> There's a twelve-hour time difference, so it's 8 o'clock in both
> places.  (from Tim Lambert.)

> ==> physics/magnets.p <==
> You have two bars of iron.  One is magnetic, the other is not.
> Without using any other instrument (thread, filings, other magnets,
> etc.), find out which is which.
> ==> physics/magnets.s <==

The proposed solution assumes that the magnetic bar is actually
magnetized.  Furthermore, it assumes it's magnetized lengthwise, rather
than (say) crosswise.

> ==> physics/resistors.p <==
> What are the resistances between lattices of resistors in the shape
> of a: [...]

The question should perhaps state explicitly that all the resistors are
equal.

> ==> physics/resistors.s <==
> 1. Cube

The reasoning given is sound, but the diagram given is not, and the
accompanying text matches the diagram rather than reality.  No
numerical answer is given, so I can't say whether this is a typo of
sorts or a true oversight.

> 	|---WWWWWW---|    |---WWWWWW---|
>    *--+---WWWWWW---+----+---WWWWWW---+---*
> 	|---WWWWWW---|    |---WWWWWW---|

The middle connection should be replaced with six resistors in
parallel, corresponding to the other six edges of the cube.  The answer
is 5/6 times the resistance of each resistor.

> ==> series/series.19.p <==
> 1 01 01011 0101101011011 0101101011011010110101101101011011 etc.
> Each string is formed from the previous string by substituting '01'
> for '1' and '011' for '0' simultaneously at each occurance.

These are switched; it should be 1->011 and 0->01.

> ==> trivia/jokes.self-referential.p <==
> What are some self-referential jokes?
> ==> trivia/jokes.self-referential.s <==

Q: Why did Douglas Hofstadter cross the road?
A: To make this riddle possible.

					der Mouse

			    mouse@larry.mcrcim.mcgill.edu