What does \upharpoonright mean?

Hello friends,

While reading the book *Representations of Finite and Compact Groups* by Barry Simon I came upon the notation $\displaystyle \upharpoonright$ which he fails to define. From context I would guess it means "restriction" but I can't be sure. For example here's some context

Quote:

Let $\displaystyle U:G\to V$ be a representation of $\displaystyle G$ on $\displaystyle V$ and suppose that $\displaystyle W\leqslant V$ is invariant under $\displaystyle U$. Then, $\displaystyle U\upharpoonright W$ and $\displaystyle U\upharpoonright W^{\perp}$ define representations $\displaystyle U_1$ and $\displaystyle U_2$ and $\displaystyle U$ is equivalent to $\displaystyle U_1\oplus U_2$