Natyashastra
अन्योन्यहेतुसंयोगः प्रसर्तव्यस्तथैव तु । योगादेककलात्सूते कनिष्ठकलयान्तरे । द्विकलान्मध्यमं चैव ज्येष्ठं चैव चतुष्कलात् ॥ ९१॥
One Kalā being added to the short [Asarita] it gives rise to the Layā (Layāntarita); and two Kalās being added [it becomes] the medium [Āsārita], and four Kalās being added [it is] the long [Āsārita].
english translation
anyonyahetusaMyogaH prasartavyastathaiva tu । yogAdekakalAtsUte kaniSThakalayAntare । dvikalAnmadhyamaM caiva jyeSThaM caiva catuSkalAt ॥ 91॥
hk transliteration by Sanscript