Yang
What is life, physically? This document provides the constitutional answer: life is the active maintenance of a constraint network --- a configuration of matter that continuously invests free-state energy ($\dot{E}_{\mathrm{main}} > 0$) to preserve its own structure against spontaneous dissolution, satisfying the Existence Inequality ($dN_c/dt \ge 0$). A living organism is a directed inverse entropy pump. It selectively couples maintenance to functional constraint configurations ($P_{\mathrm{maint}} \to 1$), creating local order while paying the irreducible tax $\tau_{\mathrm{inv}} > 1$ that guarantees global entropy increase. It operates all five constitutional operations --- Formation, Meltdown, Maintenance, Transient Event, and Capture --- as an integrated whole. It transmits constraint templates across generations through the Template Condition, making heredity a physical necessity rather than an evolutionary invention. Life is constitutionally finite. The Constrained Lifetime Theorem and the Third Arrow of Time ($dC/dt \ge 0$, CLOSED-in-EET) jointly guarantee that every organism traverses an irreversible degeneration corridor and reaches a finite $t^*$. Death is not a contingent failure but the final settlement of the inverse entropy budget --- the systemic collapse of maintenance coupling when $\mathcal{I}_{\mathrm{budget}}(t_{\mathrm{death}}) = 0$. Life is constitutionally organized. The Encapsulate operation produces nested constraint boundaries, generating hierarchical depth from the primordial membrane ($L=1$) to self-referential cognition ($L \ge 4$). Each layer adds stability at the cost of flexibility, embedding the organism's history as irreversible plastic inertia $C(t)$. Life is constitutionally normative. The Existence Inequality imposes a recursive filter: only configurations that satisfy the inequality persist. This is not ``purpose'' in any intentional sense, but the physical basis of all biological purposiveness. The continuation of Profit --- persistent existence --- is the objective toward which all living constraint operations converge. {Keywords}: Existence Inequality; active maintenance; maintenance-coupling framework; inverse entropy pump; degeneration corridor; death theorem; hierarchical depth; information architecture; constraint network metabolism; Energy-Efficiency Theory