deepen_tac: modified due to outcome of experiments.  Its choice of unsafe rule to expand is still non-deterministic.
deepen_tac: modified due to outcome of experiments.  Its
choice of unsafe rule to expand is still non-deterministic.

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