I'm reading through Lovasz's paper on discrete analytic functions but I'm confused about how the coboundary of a node $\delta v$ is defined. What does $\mathbb{R}^E$ mean on page 243 where $E$ is the set of edges of a graph. Later in the paper I see $\mathbb{R}^V$ as well where $V$ is the vertex set.
I tried looking up what $\mathbb{R}$ to the power of a set could mean but found no results.