What does an exponential with an arrow mean?

Question

Reading this article 

http://arxiv.org/pdf/0901.4937.pdf

I came across the following an expression of an exponential with a rightarrow on top

$$T(z) = \overleftarrow{\exp}\int\limits_0^{2\pi}d\sigma L \sigma(z)$$

;

(this is eq (1.91))

Answer 1

It appears to be  notation for the path-ordered exponential.   I think the arrow indicates that the smallest value of $\sigma$ appears to the right and increases as we move to the left.