English
The adjoint of a subalgebra has its underlying submodule equal to the linear span of the closure of the generating set; i.e., adjoin equals span of the closure.
Русский
У подалгебры с сопряжением подмодуль-образ равен линейному пространству замкнутого порождателя.
LaTeX
$$$\mathrm{StarAlgebra}.adjoin(R,s)^{\text{toSubmodule}} = \mathrm{span}_R(\mathrm{closure}(s \cup s^{*}))$$$
Lean4
theorem adjoin_eq_span (s : Set A) :
Subalgebra.toSubmodule (adjoin R s).toSubalgebra = span R (Submonoid.closure (s ∪ star s)) := by
rw [adjoin_toSubalgebra, Algebra.adjoin_eq_span]