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* Nailed down the "impossible match" logic.Paul Phillips2012-09-271-0/+1
I will again defer to a comment. /** Given classes A and B, can it be shown that nothing which is * an A will ever be a subclass of something which is a B? This * entails not only showing that !(A isSubClass B) but that the * same is true of all their subclasses. Restated for symmetry: * the same value cannot be a member of both A and B. * * 1) A must not be a subclass of B, nor B of A (the trivial check) * 2) One of A or B must be completely knowable (see isKnowable) * 3) Assuming A is knowable, the proposition is true if * !(A' isSubClass B) for all A', where A' is a subclass of A. * * Due to symmetry, the last condition applies as well in reverse. */