more explicit error on malformed abstract equation; dropped dead code; tuned signature
more explicit error on malformed abstract equation; dropped dead code; tuned signature

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