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Complexitylib.Algebraic.LowerBound.Cutwidth.Aggregate.Geometry.Fiber.Conditional.OneWay

Conditional entropy of actual one-way messages #

A fixed-size receiving set retains a weighted collection of narrow and wide summaries. The unmatched disjoint pairs lose at most one member per receiver coordinate, so their majority event supports all three information savings.

theorem Algebraic.Cutwidth.Aggregate.Geometry.Fiber.Conditional.card_subtype_fiber_le {X : Type u_1} {Y : Type u_2} [Fintype X] (event : Finset X) (key : X → Y) (y : Y) :
{x : ↥event | key ↑x = y}.card ≤ {x : X | key x = y}.card

Restricting the domain of a message cannot enlarge its fibers.

Conditional entropy strengthens the sender bound on the same majority event.