I agree with Nick and John. On Fri, May 23, 2008 at 12:45 PM, Robert Miller <[EMAIL PROTECTED]> wrote: > > Hello, > > During the last bug day, I found several tickets related to > inconsistencies in abelian groups. I think I've fixed the circular > logic, etc. causing the problems in the patch included in #1284. > However, there is a difference of opinion on notation that I need to > ask about here. > > Q: Should the output of > sage: G <= H > for G and H abelian groups be whether G is a subgroup of H? > > I know the answer seems simple, but here's why you might want to > answer no (William suggested this to me). If you have a list of > abelian groups L = [G1,...,Gn], and you want to quickly sort it, if > you do sorted(L), you may not get back what you are expecting, since > the subgroup ordering on abelian groups isn't linear. > > gfurnish proposes the alternative sorted(L, > cmp=canonical_ab_group_cmp), with G <= H returning whether G is a > subgroup of H. I think I favor this approach. > > The other option is G.is_subgroup(H). > > >
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