Lyapunov: |δx(t)| ~ e^{λt}
Sinai (1970): hyperbolic
billiards are ergodic
Bounces: 0
Lyapunov est: –
Billiards in Sinai's table (square with circular obstacle) are provably chaotic — nearby trajectories diverge exponentially. This is the simplest model of deterministic chaos through geometric focusing, foundational to ergodic theory and quantum chaos.