def normalize(domain)
			# strip off the protocol (\w{1,20}://), the URI (/), parameters (?), port number (:), and username (.*@)
			# then split into parts via the .
			parts = domain.gsub(/^\w{1,20}:\/\//,'').gsub(/[\/\?\:].*/,'').gsub(/.*?\@/,'').split(/\./)
			# grab the last two parts of the domain
			dom = parts[-2,2].join(".")
			# if the dom is in the two_level_tld list, then use three parts
			if @two_level_tld.index(dom)
				dom = parts[-3,3].join(".")
			end
			if @three_level_tld.index(dom)
				dom = parts[-4,4].join(".")
			end
			dom
		end
def normalize(domain)
			# strip off the protocol (\w{1,20}://), the URI (/), parameters (?), port number (:), and username (.*@)
			# then split into parts via the .
			parts = domain.gsub(/^\w{1,20}:\/\//,'').gsub(/[\/\?\:].*/,'').gsub(/.*?\@/,'').split(/\./)
			# grab the last two parts of the domain
			dom = parts[-2,2].join(".")
			# if the dom is in the two_level_tld list, then use three parts
			if @two_level_tld.index(dom)
				dom = parts[-3,3].join(".")
			end
			if @three_level_tld.index(dom)
				dom = parts[-4,4].join(".")
			end
			dom
		end
Converts a hostname to the domain: e.g., www.google.com => google.com, science.somewhere.co.uk => somewhere.co.uk