English: A causal diamond in a maximally symmetric spacetime for a ball-shaped spacelike region Σ. The past and future vertices of the diamond are denoted by p and p´, respectively, and ${\displaystyle {\mathcal {H}}}$ is the null boundary. The dashed arrows are the flow lines of the conformal Killing vector ζ, whose flow sends the boundary of the diamond into itself, and vanishes at ∂Σ,p and p´.