proposition: Lemma rext_r_trans r n (E F K : {subfield L}) x : r.-ext E F -> r F x n -> r.-ext E << F; x>>%VS.
proof: Proof. by move=> rEF /rext_r; apply: rext_trans. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_fingroup all_algebra) mathcomp(all_solvable all_field polyrcf) Abel(various classic_ext map_gal algR) Abel(char0 cyclotomic_ext real_closed_ext)