src/Pure/Thy/thy_output.ML

 end;
 
 
 (* embedded lemma *)
 
-val _ = Keyword.keyword "by";
+val _ = Keyword.declare "by" NONE;  (*overlap with command category*)
 
 val _ =
   Context.>> (Context.map_theory
    (antiquotation (Binding.name "lemma")
     (Args.prop -- Scan.lift (Args.$$$ "by" |-- Method.parse -- Scan.option Method.parse))