Seven Stars Robbery

Seven Stars Robbery
  This refers to the application of the transformations of the pre-heaven and post-heaven Eight Trigrams. For example, in the Upper Yuan, the One White Commander is strong, and both the Two Black and Seven Red are also strong. Therefore, the Two Black can seize the energy of One White for use, and Seven Red can also seize the energy of One White for use.

Similarly, in the Upper Yuan with Three Green as Commander, both Eight White and Nine Purple in the Lower Yuan are also strong. Therefore, Eight White can seize the energy of Three Green for use, and Nine Purple can also seize the energy of Three Green for use. As for other cases… they follow suit without further elaboration. This is a method where one hexagram connects to all eight hexagrams; it is truly the application of Seven Stars Robbery.
Excerpt from Geography Arena