English
If I' is a right fixed point and I ≤ I', then leftDual(rightDual(I)) ≤ I'.
Русский
Если I' — правый фиксированный пункт и I ≤ I', тогда leftDual(rightDual(I)) ≤ I'.
LaTeX
$$$\forall I,I' \subseteq \beta,\ I' \in R.\mathrm{rightFixedPoints} \land I \subseteq I' \Rightarrow R.\mathrm{leftDual}(R.\mathrm{rightDual} I) \subseteq I'.)$$$
Lean4
theorem leftDual_rightDual_le_of_le {I I' : Set β} (h : I' ∈ R.rightFixedPoints) (h₁ : I ≤ I') :
R.leftDual (R.rightDual I) ≤ I' := by
rw [← h]
apply R.gc_leftDual_rightDual.monotone_l
apply R.gc_leftDual_rightDual.monotone_u
exact h₁