added (my own version of) nonempty_sort: sg -> (string * sort) list -> sort   -> bool;
added (my own version of) nonempty_sort: sg -> (string * sort) list -> sort
  -> bool;

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