Natyashastra
प्रवृत्तमवगाढं च द्विविधं सृत्व(वृत्त)मुच्यते । आरोहित्वादवगाढं प्रवृत्तमवरोहतः ॥ १८४॥
The Vṛtta is of two kinds: Pravṛtta and Avagāḍha. The Avagāḍha arises from an ascending sequence, while the Pravṛtta arises from a descending sequence.
english translation
pravRttamavagADhaM ca dvividhaM sRtva(vRtta)mucyate । ArohitvAdavagADhaM pravRttamavarohataH ॥ 184॥
hk transliteration by Sanscript