feat(field_theory/adjoin): `intermediate_field.to_subalgebra` distributes over supremum (#10937)
feat(field_theory/adjoin): `intermediate_field.to_subalgebra` distributes over supremum (#10937)

This PR proves `(E1 ⊔ E2).to_subalgebra = E1.to_subalgebra ⊔ E2.to_subalgebra`, under the assumption that `E1` and `E2` are finite-dimensional over `F`.



Co-authored-by: tb65536 <25c750517795e47f172dc8c552ed72c7de260bd4@users.noreply.github.com>

leanprover-community/mathlib,leanprover-community/mathlib