code: public static String prettyType(int degree, Type t) {
          StringBuilder b = new StringBuilder();
          for (int i = degree; i > 0; i--) {
              b.append("set<");
          }
          b.append(t.toString().toLowerCase());
          for (int i = 0; i < degree; i++) {
              b.append(">");
          }
          return b.toString();
      }
docs: Pretty textual representation of a given element type.
  
  @param degree 0 for a literal, 1 for a set, 2 for a set of sets, ...
  @param t      the literal
  @return a String