added of_sort_proof according to krauss/schropp, with slightly more direct canonical_instance;
added of_sort_proof according to krauss/schropp, with slightly more direct canonical_instance;

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