added class_error and exception CLASS_ERROR (supercedes DOMAIN); clarified of_class_derivation; tuned witness_sorts;
added class_error and exception CLASS_ERROR (supercedes DOMAIN);
clarified of_class_derivation;
tuned witness_sorts;

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