English
Let R be a relation R: α → β → Prop. If α is empty and β is empty, then BiTotal R holds.
Русский
Пусть R — отношение α → β → Prop. Если оба домена пусты, то BiTotal(R) выполняется.
LaTeX
$$$ [\operatorname{IsEmpty}(\alpha)] \land [\operatorname{IsEmpty}(\beta)] \Rightarrow \operatorname{BiTotal}(R) $$$
Lean4
@[simp]
theorem biTotal_empty [IsEmpty α] [IsEmpty β] : BiTotal R :=
⟨leftTotal_empty R, rightTotal_empty R⟩