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Defining language | Kleene closure | String | Sigma | Alphabet set | Easy Learning Classroom

Defining language | Kleene closure | String | Sigma | Alphabet set | Easy Learning Classroom

* Rules defined explicitly and clearly
* No ambiguities
* Universally uniform understanding
* Lets the machine
- Interpret an input uniformly every time. i.e. always produces the same output for a particular input
- Explicitly reject invalid input

* Define alphabet set
* Define rules for forming valid words and sequences of words from Sigma
Called grammar, Can be descriptive , Can be mathematical, Can also define supporting functions e.g., length(X), reverse(x)

Strings: A string a finite sequence of symbols chosen from the alphabet.
For example: 0111100 , 123045, abbbcdeg etc.

* Set closure
* Kleene Closure (applied to )
- A set of all the strings (finite) that can be formed by the elements of  where the elements may be repeated any number of times.
- Denoted by Sigma/∑*
- Also called Kleene star.

Sigma/∑* : The set of all strings over an alphabet ∑ and called Kleene Star Closure of alphabet. So we have
Sigma/∑* = ∑0 U ∑1 U ∑2 U ∑3 U……………
Sigma/∑+ : The set of all strings over an alphabet ∑ excluding empty string, ε, and called plus operation. So we have
Sigma/∑+ = ∑1 U ∑2 U ∑3 U……………

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 This site provides links to random videos hosted at YouTube, with the emphasis on random.

 The original idea for this site actually stemmed from another idea to provide a way of benchmarking the popularity of a video against the general population of YouTube videos. There are probably sites that do this by now, but there wasn’t when we started out. Anyway, in order to figure out how popular any one video is, you need a pretty large sample of videos to rank it against. The challenge is that the sample needs to be very random in order to properly rank a video and YouTube doesn’t appear to provide a way to obtain large numbers of random video IDs.

 Even if you search on YouTube for a random string, the set of results that will be returned will still be based on popularity, so if you’re using this approach to build up your sample, you’re already in trouble. It turns out there is a multitude of ways in which the YouTube search function makes it very difficult to retrieve truly random results.

 So how can we provide truly random links to YouTube videos? It turns out that the YouTube programming interface (API) provides additional functions that allow the discovery of videos which, with the right approach, are much more random. Using a number of tricks, combined some subtle manipulation of the space-time fabric, we have managed to create a process that yields something very close to 100% random links to YouTube videos.

 YouTube is an American video-sharing website headquartered in San Bruno, California. YouTube allows users to upload, view, rate, share, add to playlists, report, comment on videos, and subscribe to other users. It offers a wide variety of user-generated and corporate media videos. Available content includes video clips, TV show clips, music videos, short and documentary films, audio recordings, movie trailers, live streams, and other content such as video blogging, short original videos, and educational videos. Most content on YouTube is uploaded by individuals, but media corporations including CBS, the BBC, Vevo, and Hulu offer some of their material via YouTube as part of the YouTube partnership program. Unregistered users can only watch videos on the site, while registered users are permitted to upload an unlimited number of videos and add comments to videos. Videos deemed potentially inappropriate are available only to registered users affirming themselves to be at least 18 years old.

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 YouTube has faced criticism over aspects of its operations, including its handling of copyrighted content contained within uploaded videos, its recommendation algorithms perpetuating videos that promote conspiracy theories and falsehoods, hosting videos ostensibly targeting children but containing violent and/or sexually suggestive content involving popular characters, videos of minors attracting pedophilic activities in their comment sections, and fluctuating policies on the types of content that is eligible to be monetized with advertising.

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