  Many cyber-physical systems (CPS) are safety-critical, so it is important to
formally verify them, e.g. in formal logics that show a model's correctness
specification always holds. Constructive Differential Game Logic (CdGL) is such
a logic for (constructive) hybrid games, including hybrid systems. To overcome
undecidability, the user first writes a proof, for which we present a
proof-checking tool.
  We introduce Kaisar, the first language and tool for CdGL proofs, which until
now could only be written by hand with a low-level proof calculus. Kaisar's
structured proofs simplify challenging CPS proof tasks, especially by using
programming language principles and high-level stateful reasoning. Kaisar
exploits CdGL's constructivity and refinement relations to build proofs around
models of game strategies. The evaluation reproduces and extends existing case
studies on 1D and 2D driving. Proof metrics are compared and reported
experiences are discussed for the original studies and their reproductions.
