English
For a,b : ∀ i, α(i), the size of Ioc(a,b) equals the product of the coordinatewise Icc sizes minus 1: #(Ioc a b) = ∏ i #(Icc(a(i), b(i))) − 1.
Русский
Для функций a,b: ∀ i, α(i) выполняется: |Ioc(a,b)| = (∏ᵢ |Icc(a(i), b(i))|) − 1.
LaTeX
$$$$ \\#(Ioc(a,b)) = \\prod_{i} \\#(Icc(a(i), b(i))) - 1 $$$$
Lean4
theorem card_Ico : #(Ico a b) = ∏ i, #(Icc (a i) (b i)) - 1 := by rw [card_Ico_eq_card_Icc_sub_one, card_Icc]