[GAP Forum] AddRule in KnuthBendixRewritingSystem

[Hulpke,Alexander]

Dear Forum, Dear Carl-Fredrik Brodda,

I am having issues with the AddRule() function for KnuthBendixRewritingSystems, in that I cannot get it to work at all. I am using GAP 4.11.0

At the moment, `AddRule` is declared (presumably for future addition), but there is no method implemented at all. Only `AddRuleReduced` is available My guess is that this is because the reason for adding rewriting systems to GAP was to get reduced rewriting systems

(From the declaration, I would argue that `AddRule` should take a list of monoid elements, while `AddRuleReduced` takes a lists of words given as integer lists.)

works perfectly well, and adds the rule F.1*F.1 -> F.1 to the system, even though it should take exactly the same arguments as AddRule. The command "AddRuleReduced", however, imposes an ordering on the added rule, which I do not want, so I cannot use this.

I’m unsure I understand this. The current design of rewriting systems in GAP inherently requires an ordering, and will have the rules reduce with respect to this ordering.

Your best bet might be to look into the code in lib/kbsemi.gi for `CreateKnuthBendixRewritingSystem` and `AddRuleReduced` and write your own function to add rules as-given to a rewriting system.

Best,

   Alexander Hulpke




What is going wrong here?

Best,
Carl-Fredrik Nyberg Brodda


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– Colorado State University, Department of Mathematics, Weber Building, 1874 Campus Delivery, Fort Collins, CO 80523–1874, USA email: hulpke at colostate.edu, http://www.math.colostate.edu/~hulpke