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);
src/Pure
src/FOL
src/HOL
src/ZF
src/CCL
src/CTT
src/Cube
src/FOLP
src/LCF
src/Sequents
src/Doc