Changes to 0.5:
o bug fixes in ordering function and as.character.cset
Changes to 0.4:
o fuzzy function generators added
o extended plotting for fuzzy sets added
o several functions for memberships transformation added
o performance of matching operator improved
o optional universes for gsets added
Changes to 0.3:
o support for customizable sets (cset) added
Changes to 0.2-1:
o set_options() added
Changes to 0.2:
o A *lot* of bug fixes
o closure and reduction of sets added
Changes to 0.1:
Initial release, implementing data structures and methods for
o ordinary sets
o generalized sets (fuzzy sets, multisets, fuzzy multisets)
o as well as support for fuzzy logic.