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“on H (H). Then we replace Φ : X 99K X′ by Φ ◦ ψ−1 1 : X1 99K X′ and repeat the process. The Sarkisov degree (μ, λ, e) is designed to prove the termination. The invariant (nef threshold) μ lies in a discrete set due to the boundedness of Fano varieties. The invariants (canonical threshold) λ and (the number of crepant divisors) e are related to the singularities of KX with respect to H. The Sarkisov degree drops after the replacement, and the Sarkisov program terminates after finitely many ste” (Wang 和 Chen, p. 2)