I don't think it is a script capital G, but I admit it is arguable. One of
the reasons is that the related variables s and μ are not script capital.
If you're interested, I could check in the book if script capital are used
in this book for other notations.
Le mar. 28 mars 2017 à 18:52, "Jörg Knappen" <jknap...@web.de> a écrit :
This is a script capital G or, in TeX notation, {\cal G}. It reflects the
use of multiple styles of the same underlying alhabet in mathematics and
sciences.
It is not a capital script g (note the different ordering of capital and
script).
--Jörg Knappen
I had found in 2013 a GꞬ contrast in mathematical notations of an old
(1952) physics book (see
http://www.unicode.org/mail-arch/unicode-ml/y2013-m01/0092.html)
Frédéric
