English
If U ⊆ V and f is conservative on V, then f is conservative on U.
Русский
Если U ⊆ V и f консервативна на V, то она консервативна и на U.
LaTeX
$$$\\text{If } U \\subseteq V \\text{ and } \\operatorname{IsConservativeOn}(f,V), \\text{ then } \\operatorname{IsConservativeOn}(f,U).$$$
Lean4
/-- A function `f` `IsExactOn` in `U` if it is the complex derivative of a function on `U`.
In complex variable theory, this is also referred to as "having a primitive". -/
def IsExactOn (f : ℂ → E) (U : Set ℂ) : Prop :=
∃ g, ∀ z ∈ U, HasDerivAt g (f z) z