English
Inserting an element preserves the well-foundedness of the set under a given order.
Русский
Вставка элемента сохраняет хорошо основанность множества относительно данного порядка.
LaTeX
$$$\\operatorname{WellFoundedOn}(\\operatorname{insert} a\\, s, r) \\Leftrightarrow \\operatorname{WellFoundedOn}(s, r)$$$
Lean4
@[simp]
theorem wellFoundedOn_insert : WellFoundedOn (insert a s) r ↔ WellFoundedOn s r := by
simp only [← singleton_union, wellFoundedOn_union, wellFoundedOn_singleton, true_and]