English
In a preorder, the lower bounds of s ∪ t are exactly the intersection of lower bounds of s and lower bounds of t.
Русский
В предореуденном множество нижние границы s ∪ t равны пересечению нижних границ s и нижних границ t.
LaTeX
$$$\\mathrm{lowerBounds}(s \\cup t) = \\mathrm{lowerBounds}(s) \\cap \\mathrm{lowerBounds}(t)$$$
Lean4
@[simp]
theorem lowerBounds_union : lowerBounds (s ∪ t) = lowerBounds s ∩ lowerBounds t :=
@upperBounds_union αᵒᵈ _ s t