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From: | Christian Aistleitner |
Subject: | Re: [Aldor-l] Re: [Axiom-developer] operations working in general, but not in special cases -- help needed |
Date: | Wed, 05 Apr 2006 09:49:58 +0200 |
User-agent: | Opera M2/8.52 (Linux, build 1631) |
Hi Bertfried,
Category Matroid expoerts dual then Category GraphMatroid inherits Matroid =>modifies dual -> dual= if has planar then dual else error exports new functionality
thereby, you would demolish the semantics of the dual of Matroid.I would strongly discourage from using such a solution. (Compare covariance and contravariance for parameters) If I understood you correctly, right now such a solution is not possible in Axiom anyways. And this is actually good!
According to Martin's description of matroids and "graphical matroids", a "graphical matroid" is _not_ a matroid. So a "graphical matroid" should _not_ be modelled as a specialisation of matroid.
-- King regards, Christian
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