Now that we understand the kinematics of duos and trios of mechanical quantities, we can introduce quartets. A pair produces a regime, dividing space-time in two, while a non-aligned trio gives rise to an event radiating in three directions. A quartet creates a richer structure, a network of events, populating a domain of space-time where events interact through a web of regimes—a stitch in the fabric of space-time. What was once a lonely road with a pair, and a crossroads with a trio, becomes a playground of multiple paths unfolding through a succession of events.