English
The universal property for rationals states that (∃ r, p r) is equivalent to ∃ a,b ∈ ℤ with b ≠ 0 and p(a/b).
Русский
Унитарное свойство рациональных чисел: (∃ r, p r) эквивалентно ∃ a,b ∈ ℤ, b ≠ 0 и p(a/b).
LaTeX
$$$\\forall \\{p : \\mathbb{Q} \\to \\text{Prop}\\},\\ (\\exists r, p r) \\iff \\exists a,b : \\mathbb{Z},\\ b \\neq 0 \\land p\\left(\\frac{a}{b}\\right)$$$
Lean4
protected theorem «forall» {p : ℚ → Prop} : (∀ r, p r) ↔ ∀ a b : ℤ, b ≠ 0 → p (a / b)
where
mp h _ _ _ := h _
mpr h q := by simpa [num_div_den] using h q.num q.den (mod_cast q.den_ne_zero)