I.V. Sirov on Pratt and Dowd

[Vaughan Pratt]

On Thursday, December 9, 2021 8:12 PM, Joe Shipman asked FOM for a
bijection between the rationals and the natural numbers that was computable
in polynomial time in both directions, which I answered a few days later by
using the Farey sequence to give a recursive algorithm from nats to rats
and an iterative algorithm from rats to nats, both taking polynomial time.
While working on it I consulted Don Knuth, who told me about the larger
Stern-Brocot sequence, of which the Farey sequence is the portion in the
interval (0,1).

Just now I.V. Sirov commented on recent posts to FOM by Martin Dowd and me
concerning definitions of God.  Wondering who he was, I found him (if it's
the same person) on Neil Sloane's Encyclopedia of Integer Sequences as the
creator of this intriguing enumeration of the positive rationals
<https://oeis.org/A287732/a287732_1.png>.  (1/7 connects to the next part,
omitted.)

So if these two are one, then someone out there shares my interests in
number theory and ontological/cosmological arguments.

But I also found an I.V. Serov as the principal author of this 2001 paper
on "Mantle sources of the kimberlite volcanism of the Siberian platform"
<https://repository.geologyscience.ru/handle/123456789/25571>.  Surely a
different person, but if not it's a third common interest--I'm a life
member of the American Geophysical Union and have been working in Global
Environmental Change <http://clim8.stanford.edu/> since 2011.  I'll be
speaking briefly by zoom at a side event of the final week of COP27 this
Thursday on quantifying the logistical obstacles to limiting global warming.

(And while I'm here let me piggyback the obvious correction to my earlier
post replying to Martin Dowd where I claimed that properties of Chu spaces
are represented by their covariant part, which should have been the
contravariant part.)

Vaughan Pratt
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