Source: https://www.researchgate.net/profile/Georges-Gras/publication/238882424_Sur_les_l-classes_d'ideaux_des_extensions_non_galoisiennes_de_Q_de_degre_premier_impair_l_a_cloture_galoisienne_diedrale_de_degre_2l/links/0c960533d2530c5fc2000000/Sur-les-l-classes-dideaux-des-extensions-non-galoisiennes-de-Q-de-degre-premier-impair-l-a-cloture-galoisienne-diedrale-de-degre-2l.pdf