English
An operator is closable if there exists some extension whose graph matches the closure of its graph.
Русский
Оператор близко продолжим, если существует расширение, график которого совпадает с замыканием графика оператора.
LaTeX
$$$$ \text{IsClosable}(f) \;\equiv\; \exists f' : \text{LinearPMap}, \ \mathrm{graph}(f)_{\text{top. closure}} = \mathrm{graph}(f') $$$$
Lean4
/-- An unbounded operator is closable iff the closure of its graph is a graph. -/
def IsClosable (f : E →ₗ.[R] F) : Prop :=
∃ f' : LinearPMap R E F, f.graph.topologicalClosure = f'.graph