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# ord_union(+Set1, +Set2, -Union, -New)

Computes the union and difference of Set2 and Set1

Set1
  A set
Set2
  A set
Union
  A set or variable
New
  A set or variable

## Description

Succeeds when Union is the union of Set1 and Set2, and New is the set of elements that are in Set2 but not in Set1. This is useful in order to know which elements were newly added when incrementally merging sets.

### Modes and Determinism

- ord_union(+, +, -, -) is det

## See Also

ord_disjoint_union / 3, ord_union / 3, ord_union / 2