Rationality, and MS Excel (and other calculators)

This morning, Mathieu had a nice experience in his course on computational method in actuarial science. But let us start with some mathematical formal definitions. First, recall that is – somehow – a standard expression. No one should be surprised to see such an expression. Generally (as explained in http://en.wikipedia.org/… ), this function is defined only when . The idea is that the definition of is that And it is a definition. Such a function exists only if (maybe excluding ). This would be [...]