Editing Vienna Development Method (section)

==== Sets ====
The set type constructor (written <code>set of T</code> where <code>T</code> is a predefined type) constructs the type composed of all finite sets of values drawn from the type <code>T</code>. For example, the type definition
<syntaxhighlight lang="rsl">
UGroup = set of UserId
</syntaxhighlight>
defines a type <code>UGroup</code> composed of all finite sets of <code>UserId</code> values. Various operators are defined on sets for constructing their union, intersections, determining proper and non-strict subset relationships etc.

{| border="1" class="wikitable"
|+ style="background:#ffdead;" |Main operators on sets (s, s1, s2 are sets)
|-
| <code>{a, b, c}</code> || Set enumeration: the set of elements <code>a</code>, <code>b</code> and <code>c</code>
|-
| <code><nowiki>{x | x:T & P(x)}</nowiki></code> || Set comprehension: the set of <code>x</code> from type <code>T</code> such that <code>P(x)</code>
|-
| <code>{i, ..., j}</code> || The set of integers in the range <code>i</code> to <code>j</code>
|-
| <code>e in set s</code> || <code>e</code> is an element of set <code>s</code>
|-
| <code>e not in set s</code> || <code>e</code> is not an element of set <code>s</code>
|-
| <code>s1 union s2</code> || Union of sets <code>s1</code> and <code>s2</code>
|-
| <code>s1 inter s2</code> || Intersection of sets <code>s1</code> and <code>s2</code>
|-
| <code>s1 \ s2</code> || Set difference of sets <code>s1</code> and <code>s2</code>
|-
| <code>dunion s</code> || Distributed union of set of sets <code>s</code>
|-
| <code>s1 psubset s2</code> || s1 is a (proper) subset of <code>s2</code>
|-
| <code>s1 subset s2</code>  || s1 is a (weak) subset of <code>s2</code>
|-
| <code>card s</code> || The cardinality of set <code>s</code>
|}