src/Pure/Syntax/syntax.ML

       parse_ast_translation, parse_rules, parse_translation, print_translation, print_rules,
       print_ast_translation, token_translation = _} = syn_ext;
     val {input, lexicon, gram, consts, prmodes,
       parse_ast_trtab, parse_ruletab, parse_trtab, print_trtab, print_ruletab,
       print_ast_trtab, tokentrtab, prtabs} = tabs;
-    val input' = if inout then fold (remove (op =)) xprods input else input;
+    val input' = if inout then subtract (op =) xprods input else input;
   in
     Syntax
     ({input = input',
       lexicon = if inout then Scan.make_lexicon (SynExt.delims_of input') else lexicon,
       gram = if inout then Parser.make_gram input' else gram,