 more careful exception handling in order to prevent backtracking; miscellaneous tidying up.
 more careful exception handling in order to prevent backtracking; miscellaneous tidying up.

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