====== Description ======
The union node is used to aggregate values without the prejudice inflicted by using the [[AND]] node the liberality of the [[OR]] node.  It performs a weighted average of its child-nodes.

====== Constraints ======
  * Minimum number of child-nodes: 0
  * Maximum number of child-nodes: no limit

====== Calculus ======
The union node calculates the weighted average of its child-nodes.  Weight is a node property that has meaning in only some situations.  By default its value is 1, but can be changed to any numeric value.

<m>value={sum{i=1}{n}{{value_i}*{weight_i}}}/{sum{i=1}{n}{weight_i}}</m>