Watch an assembly form. The source area has a fixed stimulus — 15 neurons firing out of 150. Through random synaptic connections, those neurons drive input into the target area. In round 1, the target winners are essentially random.
But Hebbian plasticity strengthens connections to the winners. By round 2–3, the same neurons keep winning — the assembly has converged. Green neurons are stable (won in the previous round too); cyan neurons are new winners.
This is projection: the most fundamental operation in the Assembly Calculus. It creates a stable representation of the source stimulus in the target area.