English
For every ZNum n, n.pred.succ = n.
Русский
Для любого ZNum n выполняется n.pred.succ = n.
LaTeX
$$$$\forall n:\mathrm{ZNum},\ n.\mathrm{pred}.\mathrm{succ} = n.$$$$
Lean4
@[simp]
theorem pred_succ : ∀ n : ZNum, n.pred.succ = n
| 0 => rfl
| ZNum.neg p => show toZNumNeg (pos p).succ'.pred' = _ by rw [PosNum.pred'_succ']; rfl
| ZNum.pos p => by rw [ZNum.pred, ← toZNum_succ, Num.succ, PosNum.succ'_pred', toZNum]