val my_urls = """urban""".r
def crawl(url: String, n: Int) : Unit = {
if (n == 0) ()
else if (my_urls.findFirstIn(url) == None) {
println(s"Visiting: $n $url")
get_page(url); ()
}
else {
println(s"Visiting: $n $url")
for (u <- get_all_URLs(get_page(url))) crawl(u, n - 1)
}
}