Fig. 2 .11 shows the rough numbers of types and tokens computed from some popular English corpora. The larger the corpora we look at, the more word types we find, and in fact this relationship between the number of types |V | and number of tokens N is called Herdan's Law (Herdan, 1960) or Heaps' Law (Heaps, 1978) Herdan's Law Heaps' Law after its discoverers (in linguistics and information retrieval respectively). It is shown in Eq. 2.1, where k and β are positive constants, and 0 < β < 1.