For more on Herdan's law and Heaps' Law, see Herdan (1960 , p. 28), Heaps (1978 , Egghe (2007) and Baayen (2001) ; Yasseri et al. (2012) discuss the relationship with other measures of linguistic complexity. For more on edit distance, see the excellent Gusfield (1997) . Our example measuring the edit distance from 'intention' to 'execution' was adapted from Kruskal (1983) . There are various publicly available packages to compute edit distance, including Unix diff and the NIST sclite program (NIST, 2005) .