20. al-Burhān ʻalá anna al-falak laisa huwa fī ghāyat al-ṣafāʼ ... ʻind taṣaffuḥihi li-K. Baṭlamiyūs fī al-manāẓir. [Transcribed from MS. Thurston 3, f. 93r ll.xvii-xxxviii.]