code: List<Type> erasedSupertypes(Type t) {
              ListBuffer<Type> buf = new ListBuffer<>();
              for (Type sup : closure(t)) {
                  if (sup.hasTag(TYPEVAR)) {
                      buf.append(sup);
                  } else {
                      buf.append(erasure(sup));
                  }
              }
              return buf.toList();
          }
docs: where