def urbanmain() = {

  import M3._ 
  val EVIL_urban = SEQ(STAR(STAR(CHAR('a'))), CHAR('b'))

  assert(size(der('a', der('a', EVIL_urban))) == 36)
  assert(size(der('a', der('a', der('a', EVIL_urban)))) == 83)

  assert(size(ders("aaaaaa".toList, EVIL_urban)) == 7)
  assert(size(ders(("a" * 50).toList, EVIL_urban)) == 7)
}