# What is $Pic(S)^G?$

Let $S$ be a projective surface and $\text{Pic}(S)$ its Picard group, $G$ is some group (in fact, it consists of automorpisms of $\mathbb P^2$). I came across a notation "$\text{Pic}(S)^G$". Could you explain what does it stand for?

-
There is a natural action of $G$ on $Pic(S).$ $Pic(S)^G$ is just the $G$-invariant subgroup. I'm not 100% sure of this though. – only Oct 22 '12 at 15:34