hey. this is fun and easy.

April 17, 2014 in Combinatorics, Cool Tricks, Gush

— the number of “permutations of k things
from a set of n” (“en-permute-kay”, in its
most convenient say-it-out-loud version);
the number of ways to make an (ordered)
*list* of k (distinct) things chosen from
a set of n things. one has known this from,
well, time immemorial. but never written
it out in straight-up *set* notation
until today.

now it’s on page 5 of my “bogart”.
(_introductory_combinatorics_, kenneth
p.~bogart, 1983; mine’s a recent acquisition
from the math complex, once of the
“bertha halley ross collection” according
to its bookplate. that turns out to have
been mrs. arnold ross, late of the OSU
[an all-time giant in recruiting new talent
into mathematics, founder of the “ross program”].
you can see from the edges of the pages that
somebody read it up to chapter six and stopped.
they didn’t write on the pages though.
[but that’s being put right now.])

and cranking out suchlike “set code” *is* fun
and easy… for me. showing somebody how to
*read* it? fun but *not* easy. showing some-
body how to *write* it? well… how would i
*know*? (how would *anyone*?)

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