src/HOL/Library/Abstract_Rat.thy
2008-06-26 haftmann 2008-06-26 established Plain theory and image
2008-04-02 haftmann 2008-04-02 dropped wrong code lemma
2007-10-12 wenzelm 2007-10-12 replaced syntax/translations by abbreviation;
2007-08-09 haftmann 2007-08-09 proper implementation of rational numbers