             |   |     / \   / \     |
|   |              \         /              |   |    /   \ /   \    |
|   |               \   o----------------------&gt;|   o     o     o   |
|   |                \     /      q_j       |   |    \ q_j U_j /    |
|   |                 \   /                 |   |     \       /     |
|   |                  \ /                  |   |      \     /      |
|   |                   o                   |   |       \   /       |
|   |                                       |   | 