Are Semi Direct Products Unique?
As Opposed to the Case with the Direct Product, a Semidirect Product of Two Groups Is Not, in General, Unique; If G and G′ Are Two Groups That Both Contain...
As opposed to the case with the direct product, a semidirect product of two groups is not, in general, unique; if G and G′ are two groups that both contain isomorphic copies of N as a normal subgroup and H as a subgroup, and both are a semidirect product of N and H, then it does not follow that G and G′ are isomorphic ...
Is direct product commutative?
The direct product is commutative and associative up to isomorphism. That is, G × H ≅ H × G and (G × H) × K ≅ G × (H × K) for any groups G, H, and K. The order of a direct product G × H is the product of the orders of G and H: ... This follows from the formula for the cardinality of the cartesian product of sets.
Is the product of two subgroups A subgroup?
In general, the product of two subgroups S and T is a subgroup if and only if ST = TS, and the two subgroups are said to permute.