Re: Union of two subgroups

Thanks, I'll check them out.

On Tue, Nov 17, 2020 at 7:51 AM Adam Naumowicz <[email protected]>
wrote:

> Dear Victor,
>
> On Mon, 16 Nov 2020, Victor Makarov wrote:
>
> > Dear All:
> >
> > I cannot find in MML a theorem that the union of two subgroups is  a
> > subgroup iff  one of the subgroups is a subset of the other subgroup.
> >
> > The same question about the product of two subgroups H and K:
> >
> > H*K is a subgroup iff H*K = K*H.
>
> This may not be exactly what you want, but have you checked these
> theorems:
>
> theorem :: GROUP_4:50
>    H1 "\/" H2 = gr(H1 * H2);
>
> theorem :: GROUP_4:51
>    H1 * H2 = H2 * H1 implies the carrier of H1 "\/" H2 = H1 * H2;
>
> ?
>
> Best regards,
>
> Adam Naumowicz
>
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