[texhax] Meaning of Code frag

[P. R. Stanley]

Hi
[start code]
f(x)=O(g(x))\mbox{ as }x\to a
  if and only if there exist positive numbers d and M such that
|f(x)| \le \; M |g(x)|\mbox{ for }|x - a| < \delta.
If g(x) is non-zero for values of x
[end code]

Is the | enclosing the functions used to denote order of growth?

Cheers
Paul