Join of finitely many pronormal subgroups

Definition
A subgroup $$H$$ of a group $$G$$ is termed a join of finitely many pronormal subgroups if there exist subgroups $$H_1, H_2, \dots, H_n$$ of $$G$$ (with $$n$$ a natural number) such that $$H$$ is the join of all the $$H_i$$s.