src/Pure/type.ML

      arities: Sorts.arities}
   val classes: type_sig -> class list
   val defaultS: type_sig -> sort
   val logical_types: type_sig -> string list
   val univ_witness: type_sig -> (typ * sort) option
+  val is_type_abbr: type_sig -> string -> bool
   val subsort: type_sig -> sort * sort -> bool
   val eq_sort: type_sig -> sort * sort -> bool
   val norm_sort: type_sig -> sort -> sort
   val witness_sorts: type_sig -> sort list -> sort list -> (typ * sort) list
   val rem_sorts: typ -> typ

 
 fun classes (TySg {classes = cs, ...}) = cs;
 fun defaultS (TySg {default, ...}) = default;
 fun logical_types (TySg {log_types, ...}) = log_types;
 fun univ_witness (TySg {univ_witness, ...}) = univ_witness;
+fun is_type_abbr (TySg {abbrs, ...}) name = is_some (Symtab.lookup (abbrs, name));
 
 
 (* sorts *)
 
 fun subsort (TySg {classrel, ...}) = Sorts.sort_le classrel;