In this example, we’ve defined two new speak() methods. This is called overriding a method. You override a superclass’s property with a subclass property of the same name.

An Automatic Method of Solving Discrete Programming Problems. A. H. Land and A. G. Doig. Econometrica. Vol. 28, No. 3 (Jul., 1960), pp. 497-520 (24 pages) ... Its use is illustrated on two numerical ...