Louhivaara, Ilppo Simo, and Christian G. Simader. “Über Periodische Lösungen Koerzitiver Linearer Partieller Differentialgleichungen”. Annales Fennici Mathematici 4, no. 1 (February 1, 1979): 87–108. Accessed November 25, 2024. https://afm.journal.fi/article/view/134340.