immutable theory values with full stamp record of every update (increase of stamp size for HOL: 20000 -> 100000, JinjaThreads: 65000 -> 300000) -- minimal measurable impact on inference kernel performance;
more opportunistic string_of_clause, to make double-sure its Syntax.string_of_term uncheck phase does not crash, and thus bomb ambiguous input via failed composition of warning (e.g. HOL/Imperative_HOL/ex/Linked_List.thy: lemma merge_simps);