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Equation 32 · Part 3 · The Entry a Relabeling Cannot Write

Symbol H_f

Λ†(Hc)=Hf\Lambda^\dagger(H_c) = H_f
HfH_f

What this part means

HfH_f is an input to the expression that computes the quantity on the left.

Its job in the formula

HfH_f is an input to the expression that computes the quantity on the left.

The passage around this formula

is a real number in units of energy for every fine state ρ\rho : how much the coarse description, evaluated through HcH_c pulled back along Λ\Lambda , disagrees with the fine description’s own HfH_f , for that specific state. Because expectation values determine a Hermitian operator uniquely — two Hermitian operators with the same trace against every density matrix are the same operator — the strongest statement follows at once: Δ\Delta EΛ(ρ)E_\Lambda(\rho) = 0 for every fine state ρ\rho if and…

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Learn the underlying idea

A subscript is a label attached below a symbol. It often selects a time step, component, category, or member of a sequence.

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Sources cited in the article section

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