The affixes ktvā , kta and ktvātu optionally get the iṭ augment after kliś,
As क्लिष्ठ्वा or क्लिशित्वा, क्लिष्टः or क्लिशितः, क्लिष्टवान् or क्लिषितवान् ॥ क्लिशू (IX. 50) having an indicatory ऊ would have optionally taken इट् before ktva by 7.2.44, but then the Nishtha affixes by 7.2.15 would never have taken the augment. क्लिश् (Divadi 52) उपतापे, being anudatta would always have taken इट् before ktva and Nishtha. Hence this rule ordains option with regard to ktva.,