new theorem UN_empty; it and Un_empty inserted by AddIffs
new theorem UN_empty; it and Un_empty inserted by AddIffs

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle