Section SkewField.
Hypothesis fieldT : GRing.Field.mixin_of aT.
Fact agenv_is_aspace U : is_aspace (agenv U).
Canonical agenv_aspace U : {aspace aT} := ASpace (agenv_is_aspace U).
(* Kleene algebra properties *)

Lemma subv_adjoin U x : (U <= <<U; x>>)%VS.