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 *                           RGB example                           *
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This example illustrates compile-time synthesis of types using PETE.
See the tutorial in html/tut-3.html for a description of this example.

Mathemetical operations between three `colors' (Operand<Blue>,
Operand<Red> and Operand<Green>) are implemented.  Functors are defined
that extract the types of the leaves.  The PETE class Combine2
is specialized in RGB.h to tell PETE how to combine the types in
an expression.

Type computations of this sort are often used to select particular
algorithms based on the types of the objects appearing in an expression.
