added class_error and exception CLASS_ERROR (supercedes DOMAIN);
clarified of_class_derivation;
tuned witness_sorts;
;;;
;;; $Id$
;;;
;;; Options for Proof General
;; Examples for sensible settings:
;(custom-set-variables '(isar-eta-contract nil))
;(custom-set-faces
; '(proof-locked-face
; ((((type x) (class color) (background light)) (:background "lightsteelblue2")))))