diff -r a80d8ec6c998 -r 3dda49e08b9d src/Sequents/modal.ML
--- a/src/Sequents/modal.ML	Fri Jan 04 21:49:06 2019 +0100
+++ b/src/Sequents/modal.ML	Fri Jan 04 23:22:53 2019 +0100
@@ -26,7 +26,7 @@
 struct
 
 (*Returns the list of all formulas in the sequent*)
-fun forms_of_seq (Const(@{const_name SeqO'},_) $ P $ u) = P :: forms_of_seq u
+fun forms_of_seq (Const(\<^const_name>\<open>SeqO'\<close>,_) $ P $ u) = P :: forms_of_seq u
   | forms_of_seq (H $ u) = forms_of_seq u
   | forms_of_seq _ = [];