Friday, August 13, 2010

law of trichotomy

Welcome to online math forum,
The law of trichotomy still isn't covered. It can be split into two parts: at most one of the three cases can occur, and at least one of the three cases occurs. more examples on math forum; The first can be stated as an axiom of addition as

It is not the case that x = x + y.

And that says it is not the case that x > x. The other half requires the axiom

For each x and y, either x = y or there is some z such that x + z = y, or there is some z such that x = y + z.

With these axioms, all the properties of magnitudes needed in the first few books of the Elements can be proved. For instance, we can prove

If 2x = 2y, then x = y.

more examples on free online math tutoring.

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