... x(s)isastreamline at the instantt,itisacurve parametrized by a variable, say s, that satisfiesdxds= u(x(s),t),tfixed.We define a fixed trajectory to be the curve traced out by a particleas time ... page iPrinter: Opaque this A Mathematical Introduction to Fluid Mechanics Alexandre Chorin Department of MathematicsUniversity of California, BerkeleyBerkeley, California 94720-384 0, USAJerrold ... subject to dispute. However, the physical relevance of the notion (or mathematical theorems we deduce from it) must be checked by experiment.As we shall see later, ideal fluids exclude many interesting...