improved tptp_graph robustness by relying on thy; reused cleanup code; improved messages;
improved tptp_graph robustness by relying on thy;
reused cleanup code;
improved messages;

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