handle "set" correctly in Refute -- inspired by old code from Isabelle2007
handle "set" correctly in Refute -- inspired by old code from Isabelle2007

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