set

Primitive methods (know about representation)

The representation is a table whose tags are the elements, and
whose values are true.

member: Say whether an element is in a set
  s: set
  e: element
returns
  f: true if e is in set, false otherwise

insert: Insert an element to a set
  s: set
  e: element

new: Make a list into a set
  l: list
returns
  s: set

elements: Iterator for sets
TODO: Make the iterator return only the key

High level methods (representation unknown)

difference: Find the difference of two sets
  s, t: sets
returns
  r: s with elements of t removed

difference: Find the symmetric difference of two sets
  s, t: sets
returns
  r: elements of s and t that are in s or t but not both

intersection: Find the intersection of two sets
  s, t: sets
returns
  r: set intersection of s and t

union: Find the union of two sets
  s, t: sets
returns
  r: set union of s and t

subset: Find whether one set is a subset of another
  s, t: sets
returns
  r: true if s is a subset of t, false otherwise

propersubset: Find whether one set is a proper subset of
another
  s, t: sets
returns
  r: true if s is a proper subset of t, false otherwise

equal: Find whether two sets are equal
  s, t: sets
returns
  r: true if sets are equal, false otherwise

Metamethods for sets

set - table = set difference

set * table = intersection

set / table = symmetric difference

set <= table = subset

set < table = proper subset