Maintenance work on the ZORA databases is scheduled for Wednesday 22 May 2019 from 20:00-22:00. During this period ZORA and JDB will not be available. Thank you for your understanding.
Deuel, Johanna; Hess, Peter (1976). 3.—A Criterion for the Existence of Solutions of Non-linear Elliptic Boundary Value Problems. Proceedings of the Royal Society of Edinburgh Section A: Mathematics, 74:49-54.