BaseSet 0.9.0

• tidy() now defaults to tidySet().

• New function union_closed().

• Make more robust the code to unwanted dimensions drops.

• power_set() returns also the sets of size 1 and have better names by default.

• Extractors [, $, [[ and setters [<-, $<-, [[<- now work for
  TidySets:

  • i indicates rows,
  • j either "relations", "sets" or "elements"
  • k the columns of the slot.

  However TS[["A"]] extracts set "A" and replacing it via [[<- will remove
  it.

• Completion of $ works.

• length() returns the number of sets (to complete ncol and nrow).

• lengths() returns the number of relations for each set.