English
If there exists i with p i, then swapping the order of a with the biSup over i and h is equivalent to taking the biSup over i of a ⊔ f i h.
Русский
Если существует i с p(i), то swapping the order of a и biSup over i и h эквивалентен взятию biSup по i от a ⊔ f(i,h).
LaTeX
$$$ \\big( a \\vee \\bigvee_{i} \\big( f(i,h) \\big) \\big) = \\bigvee_{i} \\big( a \\vee f(i,h) \\big). $$$
Lean4
theorem sup_biSup {p : ι → Prop} {f : ∀ i, p i → α} {a : α} (h : ∃ i, p i) :
(a ⊔ ⨆ (i) (h : p i), f i h) = ⨆ (i) (h : p i), a ⊔ f i h := by simpa only [sup_comm] using @biSup_sup α _ _ p _ _ h