Witzel has questioned the linguistic nature of the so-called Indus script (Farmer, Sproat, Witzel 2004). Farmer, Sproat, and Witzel presented a number of arguments in support of their thesis that the Indus script is non-linguistic, principal among them being the extreme brevity of the inscriptions, the existence of too many rare signs increasing over the 700-year period of the Mature Harappan civilization, and the lack of random-looking sign repetition typical for representations of actual spoken language (whether syllable-based or letter-based), as seen, for example, in Egyptian cartouches.