code: public static boolean contains(Package pack, Package wantedPackage) {
      return new PackageTreeTraverser()
          .postOrderTraversal(pack)
          .anyMatch(childPackage -> Objects.equals(childPackage, wantedPackage));
    }
docs: Looks through a {@link Package} and its children to see if the sought-after package is
  contained within.
  
  @param pack the package to explore
  @param wantedPackage the sought-after package
  @return true if the sought-after package was found