A subgroup A is called seminormal in a group G if there exists a subgroup B such that G = AB and AX is a subgroup of G for every subgroup X of B. Studying a group of the form G = AB with seminormal supersoluble subgroups A and B, we prove that
. Moreover, if the indices of the subgroups A and B of G are coprime then
. Here
,
, and
are the formations of all nilpotent, supersoluble, and metanilpotent groups respectively, while
is the
-residual of H. We also prove the supersolubility of G = AB when all Sylow subgroups of A and B are seminormal in G.