English
If n ≤ m then ofNat(n) ≤ ofNat(m).
Русский
Если n ≤ m, то ofNat(n) ≤ ofNat(m).
LaTeX
$$$ \forall {n,m : \mathbb{N}},\; n \le m \rightarrow \text{ofNat}(n) \le \text{ofNat}(m) $$$
Lean4
theorem ofNat_le_ofNat {n m : Nat} (h : n ≤ m) : ofNat n ≤ ofNat m :=
by
simp only [ofNat, ne_eq, _root_.decide_not]
cases Nat.decEq n 0 with
| isTrue hn => grind [Bool.false_le]
| isFalse hn => cases Nat.decEq m 0 with grind [Bool.le_true]