TITLE: Mathematical notation around the world
QUESTION [13 upvotes]: What are the differences in mathematical notation around the world? I know that in some other countries they write 1,2 meaning 1.2, but what else can be confusing in an academic environment (when people are doing math on a board or on paper).

REPLY [3 votes]: Function composition, in the context of group theory (a permutation is a bijection from a set onto itself), can be written
$$(fg)(x)=f(g(x))$$
Or
$$(fg)(x)=g(f(x))$$
The latter seems to be (or have been) used by some anglo-saxon mathematicians, and appears in books by Burnside, and Passman.

Also, matrix transpose is denoted $^tA$ in France, while it seems to be $A^T$ mostly everywhere else. This can be confusing when you write a product: $AB^TA^{-1}$ is of course not the same as $AB^tA^{-1}$.