ApCoCoA-1:Baumslag groups

Baumslag groups

Descrpition

Baumslag-Solitar groups have the following presentation.

BS(m,n)<a, b | ba^{m} = a^{n}b> where m, n are natural numbers

(Reference: G. Baumslag and D. Solitar, Some two generator one-relator non-Hopfian groups, Bull. Amer. Math. Soc. , 689 (1962) pp. 199–201.)

Computation

We enumerate partial Groebner bases for the Baumslag-Solitar groups as follows.

/*Use the ApCoCoA package ncpoly.*/
Use ZZ/(2)[a[1..2],b[1..2]];
NC.SetOrdering("LLEX");
Define CreateRelations()
  A1:=[[a[1],a[2]],[1]];
  A2:=[[a[2],a[1]],[1]];
  B1:=[[b[1],b[2]],[1]];
  B2:=[[b[2],b[1]],[1]];
  R:=[[b[1],a[1]^(2)],[a[1]^(3),b[1]]];
  Return [A1,A2,B1,B2,R];
EndDefine;
-- Relation ba^2=a^3b. Change 2 and 3 in "()" to make another relation
G:=CreateRelations();
-- Enumerate a partial Groebner basis (see NC.GB for more details)
NC.GB(G,31,1,100,1000);

/*Use the ApCoCoA package gbmr.*/
-- See NCo.BGB for more details on the parameters DB, LB and OFlag.
Define BS(M,N,DB,LB,OFlag)
  $apcocoa/gbmr.SetX("aAbB");
  $apcocoa/gbmr.SetOrdering("LLEX");
  G:= [["aA",""],["Aa",""],["bB",""],["bB",""]];
  BA:= "b";
  AB:= "b";
  For I:= 1 To ARGV[1] Do
    BA:= BA + "a"; 
  EndFor;
  For I:= 1 To ARGV[2] Do
    AB:= "a" + Ab; 
  EndFor;
  Append(G,[BA,AB]);
  Return $apcocoa/gbmr.BGB(G,DB,LB,OFlag);
EndDefine;