As a supplement to this treatise he wrote a second, which he called the "Kitab al-Af'al Dhawat al-Mathalain" (The Book of Verbs Containing Double Letters), and in which he points out the principles governing the verbs whose second and third radicals are alike. He furnishes a list of these verbs, together with their various forms occurring in the Bible. Besides the two treatises on verbs Hayyuj wrote "Kitab al-Tanqit" (The Book of Punctuation). This work, probably written before his two chief treatises, is an attempt to set forth the features underlying the Masoretic use of the vowels and of the word-tone. In this work he deals chiefly with nouns, and its purpose is more of a practical than of a theoretical character.