7. Cheonbugyeong_un sam sa seong hwan o chil

[運三四成環五七]
[운삼사성환오칠, un sam sa seong hwan o chil]
The movement of a cycle starts with Three and Four;
the circulation completes under Five and Seven.

What are the roles of three and four, and five and seven in the cyclical pattern of creation and transformation?