Flexible grid generation for complex geometries in two space dimensions based on variational principles / by B. Oskam and G.H. HuizingModified version of LTRAN2 : a calculation method for inviscid transonic flow about thin airfoils in moderately slow unsteady motion / by J. van der Vooren and G.H. HuizingA finite difference method for the calculation of transonic flow about a wing, based on small perturbation theory / by J. van der Vooren, G.H. Huizing and A van Essen