src/HOL/Tools/Nitpick/nitpick_nut.ML

         | (Const (@{const_name Id}, T), []) => Cst (Iden, T, Any)
         | (Const (@{const_name converse}, T), [t1]) =>
           Op1 (Converse, range_type T, Any, sub t1)
         | (Const (@{const_name trancl}, T), [t1]) =>
           Op1 (Closure, range_type T, Any, sub t1)
-        | (Const (@{const_name rel_comp}, T), [t1, t2]) =>
+        | (Const (@{const_name relcomp}, T), [t1, t2]) =>
           Op2 (Composition, nth_range_type 2 T, Any, sub t1, sub t2)
         | (Const (x as (s as @{const_name Suc}, T)), []) =>
           if is_built_in_const thy stds x then Cst (Suc, T, Any)
           else if is_constr ctxt stds x then do_construct x []
           else ConstName (s, T, Any)