krauss [Tue, 07 Nov 2006 09:33:47 +0100] rev 21199
* Added annihilation axioms ("x * 0 = 0") to axclass semiring_0.
Richer structures do not inherit from semiring_0 anymore, because
anihilation is a theorem there, not an axiom.
* Generalized axclass "recpower" to arbitrary monoid, not just
commutative semirings.