1. Loof HW (1961) Edge disturbances in a hyppar shell with straight edges, Report 8-61-3-hr-1. Stevin Laboaratory, Department of Civil Engineering, Technical University Delft (in Dutch)
2. Bouma AL (1960) Some applications of the bending theory regarding doubly curved shells. In: Proceedings of the Symposium on theory of thin shells, North Holland Publishing Company, Delft, August 1959, pp 202–235