The Creator's Words

"It may be said there are two basic criteria for a proper shell:

"The shell must be stable and of a shape which permits an easy way to work. It should be as symmetrical as possible because this simplifies its behaviour. Either interior groins (as in the restaurant in Xochimilco) or exterior edges should be able to send loads to points of support, or else there should be a continuous support along certain edges....

"A comparatively rapid, simple method must be found to calculate the membrane stresses. At the moment this seems possible only with the hypar shell, if by 'simple' one infers a procedure which mathematics, or specifically, in every case having to solve a system of differential equations to comply with previously selected boundary conditions."

— Felix Candela. from Colin Faber. Candela/The Shell Builder. p199.