improvements in LowIndexSubgroup algorithm
improvements in LowIndexSubgroup algorithm

aktech/sympy,postvakje/sympy,postvakje/sympy,sampadsaha5/sympy,jaimahajan1997/sympy,yashsharan/sympy,kaushik94/sympy,kaushik94/sympy,yashsharan/sympy,drufat/sympy,souravsingh/sympy,chaffra/sympy,chaffra/sympy,skidzo/sympy,jaimahajan1997/sympy,madan96/sympy,madan96/sympy,yashsharan/sympy,kaushik94/sympy,postvakje/sympy,jaimahajan1997/sympy,aktech/sympy,rahuldan/sympy,souravsingh/sympy,sampadsaha5/sympy,rahuldan/sympy,skidzo/sympy,madan96/sympy,aktech/sympy,rahuldan/sympy,skidzo/sympy,chaffra/sympy,sampadsaha5/sympy,drufat/sympy,drufat/sympy,souravsingh/sympy