2013-01-17 hoelzl 2013-01-17 countablility of finite subsets and rational numbers
2012-11-27 immler 2012-11-27 based countable topological basis on Countable_Set
2012-11-21 hoelzl 2012-11-21 Countable_Set: tuned lemma names; more generic lemmas
2012-11-21 hoelzl 2012-11-21 renamed BNF/Countable_Set to Countable_Type and moved its generic stuff to Library/Countable_Set
2012-11-20 hoelzl 2012-11-20 add Countable_Set theory