English
RightDual maps any set I ⊆ β to { a ∈ α | ∀ b ∈ I, a ~[R] b }.
Русский
RightDual отображает любой набор I ⊆ β в { a ∈ α | ∀ b ∈ I, a ~R b }.
LaTeX
$$$\mathrm{rightDual}(I) = \{ a \in \alpha \mid \forall b \in I,\ a \;\tilde{R}\; b \}.$$$
Lean4
/-- `rightDual` maps any set `I` of elements of type `β` to the set `{a : α | ∀ b ∈ I, a ~[R] b}`
of elements `a` of type `α` such that `a ~[R] b` for every element `b` of `I`. -/
def rightDual (I : Set β) : Set α :=
{a : α | ∀ ⦃b⦄, b ∈ I → a ~[R] b}