English
The algebra generated by the union of two sets s and t is the join of the algebras generated by each set individually: adjoin_R(s ∪ t) = adjoin_R(s) ⊔ adjoin_R(t).
Русский
Порождение над R множества s ∪ t равно объединению порождений отдельных множеств: adjoin_R(s ∪ t) = adjoin_R(s) ⊔ adjoin_R(t).
LaTeX
$$$$\\operatorname{adjoin}_R(s \\cup t) = \\operatorname{adjoin}_R(s) \\;\\amalg\\; \\operatorname{adjoin}_R(t)$$$$
Lean4
theorem adjoin_union (s t : Set A) : adjoin R (s ∪ t) = adjoin R s ⊔ adjoin R t :=
(Algebra.gc : GaloisConnection _ ((↑) : Subalgebra R A → Set A)).l_sup