`BookProof.ChapterPinDoubleCover.LamZ_fiber_card` : ∀ d ∈ Delta, (Omega.filter (fun S => LamZ S = d)).card = 2

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`BookProof.ChapterPinDoubleCover.LamZ_fiber_card` : ∀ d ∈ Delta, (Omega.filter (fun S => LamZ S = d)).card = 2 · Prove2Me