English
In a partial order with a top and bottom, IsCompl a b holds if and only if both Disjoint a b and Codisjoint a b hold.
Русский
При частичном порядке с максимумом и минимумом IsCompl a b эквивалентно тому, что одновременно верны Disjoint a b и Codisjoint a b.
LaTeX
$$$\text{IsCompl}(a,b) \iff (\text{Disjoint}(a,b) \land \text{Codisjoint}(a,b))$$$
Lean4
theorem isCompl_iff [PartialOrder α] [BoundedOrder α] {a b : α} : IsCompl a b ↔ Disjoint a b ∧ Codisjoint a b :=
⟨fun h ↦ ⟨h.1, h.2⟩, fun h ↦ ⟨h.1, h.2⟩⟩