ワイルの補題 (ラプラス方程式)
↑ Hermann Weyl, The method of orthogonal projections in potential theory, Duke Math. J., 7, 411-444 (1940). See Lemma 2, p. 415
↑ Bernard Daconorogna, Introduction to the Calculus of Variations, 2nd ed., Imperial College Press (2009), p. 148.
↑ Lars Gårding, Some Points of Analysis and their History, AMS (1997), p. 66.
↑ Lars Hörmander, The Analysis of Linear Partial Differential Operators I, 2nd ed., Springer-Verlag (1990), p.110