added all, is_all; improved dest_all; added implies (from term.ML);
added all, is_all;
improved dest_all;
added implies (from term.ML);

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