\begin{circus}
  \circchannel a
  \end{circus}
  \begin{circus}
  \circprocess P \circdef \circbegin \circspot a \then \Skip \circend \\
  \circprocess Q \circdef P \lpar \lchanset a \rchanset \rpar P \\
  \circprocess R \circdef Q \lpar \lchanset a \rchanset \rpar P \\
  \end{circus}