addition

The passage around this formula

An abstract recurrence makes the retention problem visible: $C_{t+1}=\rho_t C_t + I_t - L_t$. where $C_t$ is usable cultural complexity, $\rho_t$ is effective transmission fidelity, $I_t$ is validated innovation, and $L_t$ is loss from population disruption, inaccessible records, incompatible standards, or failed teaching. Innovation receives most historical attention, but cumulative growth requires $\rho_t$ to remain high enough that new work does not merely reconstruct forgotten prerequisites.

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