1 

     2 val EVIL_urban = SEQ(STAR(STAR(CHAR('a'))), CHAR('b'))

     3 

     4 assert(size(der('a', der('a', EVIL_urban))) == 28)

     5 assert(size(der('a', der('a', der('a', EVIL_urban)))) == 58)

     6 

     7 assert(size(ders("aaaaaa".toList, EVIL_urban)) == 8)