title: Compute trigram probability from bigrams probabilities
body: <p>Given <code>bigram probabilities</code> for words in a text, how would one compute <code>trigram probabilities</code>? </p>
  
  <p>For example, if we know that <code>P(dog cat) = 0.3</code> and <code>P(cat mouse) = 0.2</code> </p>
  
  <p>how do we find the probability of <code>P(dog cat mouse)</code>?</p>
  
  <p>Thank you!</p>