Two small and independent interrogative remarks:
(1) Nowadays, an extension of a group G by a group K is a group H fitting in a short exact sequence
$latex 1\rightarrow K\rightarrow H\rightarrow G\rightarrow 1$
in other words, and rather counterintuitively, the group G is a quotient of the group which is the extension. When did this terminology originate? A paper of Alan Turing (entitled, rather directly, “The extensions of a group”) defines “extension”, in the very first paragraph, exactly in the opposite (naïve) way, quoting Schreier and Baer who, presumably, had the same convention.
(2) There’s a whole lot of discussion here and there about the mystical “field with one element”; usually, papers of Tits from around 1954 are mentioned as being the source of the whole “idea”; however, the following earlier quote from a 1951 paper of R. Steinberg (“A geometric approach to the representations of the full linear group over a Galois field”, 1951, p. 279, TAMS 71, 274–282) seems to also contain a germ of the often mentioned analogy between the formulas for the order of the Weyl groups and those of groups of Lie type over a field with q elements, the former being obtained by specializing the latter for q=1:
In closing this section, a remark on the analogy between G and H seems to be in order. Instead of considering G as a group of linear transformations of a vector space, we could consider G as a collineation group of a finite (n-1)-dimensional geometry. If q=1, the vector space fails to exist but the finite geometry does exist and, in fact, reduces to the n vertices of a simplex with a collineation group isomorphic to H. “
In this citation, G is GL(n,Fq), and H is the symmetric group on n letters.
(3) Here’s a third question: when did the terminology “Galois field” become more or less obsolete within the pure mathematics community?
