ApCoCoA-1:Baumslag-Gersten groups
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Description
The Baumslag-Gersten groups have a Dehn function growing faster than any fixed iterated tower of exponentials and can be represented as:
BG = <a,b | (b^{-1}a^{-1}b)a(b^{-1}a^{-1}b) = a^{2}>
Reference
A. N. Platonov, An isoparametric function of the Baumslag-Gersten group. (in Russian.) Vestnik Moskov. Univ. Ser. I Mat. Mekh. 2004, , no. 3, pp. 12–17; translation in: Moscow University Mathematics Bulletin, vol. 59 (2004), no. 3, pp. 12–17 (2005).
Computation
We enumerate partial Groebner bases for the Baumslag-Gersten groups as follows.
/*Use the ApCoCoA package ncpoly.*/ Use ZZ/(2)[a,b,c,d]; NC.SetOrdering("LLEX"); Define CreateRelationsBaumslagGersten() Relations:=[]; // Add the relations of the inverse elements ac = ca = 1 and bd = db = 1 Append(Relations,[[a,c],[1]]); Append(Relations,[[c,a],[1]]); Append(Relations,[[b,d],[1]]); Append(Relations,[[d,b],[1]]); // Add the relation (b^{-1}a^{-1}b)a(b^{-1}a^{-1}b = a^2) Append(Relations,[[d,c,b,a,d,c,b],[a^2]]); Return Relations; EndDefine; Relations:=CreateRelationsBaumslagGersten(); Relations; -- Enumerate a partial Groebner basis (see NC.GB for more details) Gb:=NC.GB(Relations,31,1,100,1000); Gb;
Example in Symbolic Data Format
<FREEALGEBRA createdAt="2014-01-20" createdBy="strohmeier"> <vars>a,b,c,d</vars> <uptoDeg>11</uptoDeg> <basis> <ncpoly>a*c-1</ncpoly> <ncpoly>c*a-1</ncpoly> <ncpoly>b*d-1</ncpoly> <ncpoly>d*b-1</ncpoly> <ncpoly>d*c*b*a*d*c*b-a*a</ncpoly> </basis> <Comment>The partial LLex GB has 201 elements</Comment> <Comment>Baumslag-Gersten_group</Comment> </FREEALGEBRA>