The function f is idempotent, if f(x) = f(f(x)). For this URL shortener, if http://www.5z8.info/super-nsfw_g0v1ba_hot-older-goats.mov http://www.5z8.info/super

The function f is idempotent, if f(x) = f(f(x)). For this URL shortener, if http://www.5z8.info/super-nsfw_g0v1ba_hot-older-goats.mov http://www.5z8.info/super-nsfw_g0v1ba_hot-older-goats.mov (from above) points to http://shadyurl.com/ http://shadyurl.com/, then shortening http://www.5z8.info/super-nsfw_g0v1ba_hot-older-goats.mov http://www.5z8.info/super-nsfw_g0v1ba_hot-older-goats.mov should also return http://www.5z8.info/super-nsfw_g0v1ba_hot-older-goats.mov http://www.5z8.info/super-nsfw_g0v1ba_hot-older-goats.mov. It's not enough for it to always return the same URL for the same input (which it also doesn't appear to do).