A two-dimensional example of these features subject to the constraint “omega equals k-squared psi” is the Lamb–Chaplygin dipole. Motion near “lines” of these features is described by three theorems devised by Helmholtz, which are proven (-5[1])using a theorem named for Kelvin. The Strouhal number is defined by the rate of “shedding” of these features, which generate a “street” named for von Karman. (10[1])A (10[1])set of three of these features that form a characteristic horseshoe shape surround an aircraft wing. A quantity named (10[1])for these features is defined as the curl of flow velocity, whose surface integral is circulation. Small examples of these features are called (10[1])eddies. (-5[2])For 10 points, name these swirling (-5[1])features in a fluid flow exemplified by tornadoes and whirlpools. ■END■ (10[4])