Quotient Epimorphism Condition for Normal Subgroup Product to be Internal Group Direct Product/Necessary Condition

Theorem
Let $\struct {G, \odot}$ be a group

Let $\struct {H, \odot}$ and $\struct {K, \odot}$ be normal subgroups of $\struct {G, \odot}$.

Let:
 * the restriction of the quotient epimorphism $q_H$ to $K$ be an isomorphism from $K$ onto the quotient group $G / H$

and:
 * the restriction of the quotient epimorphism $q_K$ to $H$ be an isomorphism from $H$ onto the quotient group $G / K$

Then $\struct {G, \odot}$ is the internal group direct product of $\struct {H, \odot}$ and $\struct {K, \odot}$,