If $\mathbb v$ denotes the velocity of a point $s$ in $\mathbb R^3$, what is $\mathbb R^3\{\mathbf v\}$? (notation)

Question

I started reading 'Mathematical Aspects of Classical and Celestial Mechanics' by Vladimir Arnold (Third Edition). In page $2$ they say that the euclidean space is denoted by $E^3$; moreover:

The set $E^3$ is also called the configuration space of the point $s$. The pair $(s,\mathbf v)$ is called the state of the point, and the set $E^3\times\mathbb R^3\{\mathbf v\}$, the phase (or state) space.

I've never seen the notation $A\{x\}$, what does it mean?

Thanks a lot!