English
For all m,n in PosNum, (m : ℕ) < n ↔ m < n.
Русский
Для любых m,n из PosNum, (m : ℕ) < n эквивалентно m < n.
LaTeX
$$$(m : \\mathbb{N}) < n \\iff m < n$$$
Lean4
@[norm_cast]
theorem lt_to_nat {m n : PosNum} : (m : ℕ) < n ↔ m < n :=
show (m : ℕ) < n ↔ cmp m n = Ordering.lt from
match cmp m n, cmp_to_nat m n with
| Ordering.lt, h => by simp [h]
| Ordering.eq, h => by simp [h]
| Ordering.gt, h => by simp [not_lt_of_gt h]