English
Erasing the minimum in a tree corresponds to erasing the maximum in the dual tree: dual (eraseMin t) = eraseMax (dual t).
Русский
Удаление минимального элемента в дереве соответствует удалению максимального в двойственном дереве: dual (eraseMin t) = eraseMax (dual t).
LaTeX
$$$\operatorname{dual}(\operatorname{eraseMin}(t)) = \operatorname{eraseMax}(\operatorname{dual}(t))$$$
Lean4
theorem dual_eraseMin : ∀ t : Ordnode α, dual (eraseMin t) = eraseMax (dual t)
| nil => rfl
| node _ nil _ _ => rfl
| node _ (node sz l' y r') x r => by
rw [eraseMin, dual_balanceR, dual_eraseMin (node sz l' y r'), dual, dual, dual, eraseMax]