Stichting Mathematisch Centrum
Stichting Mathematisch Centrum. Toegepaste Wiskunde

Veltkamp, G. W. (1956). The behaviour of a solution of Helmholtz' equation near a confluence of boundary-conditions, involving directional derivatives. In Stichting Mathematisch Centrum. Toegepaste Wiskunde (TW 40/56). Stichting Mathematisch Centrum.