The participial affix does not take the augment iṭ after the root kaṣ when the participle means 'difficult' and 'impenetrable'.,
As कष्टोऽग्निः, कष्टं व्याकरणं, ततोऽपि कष्टतराणि सामानि ॥ \Difficult is Fire-sacrifice i. e. it is difficult to completely master the ritual connected with the worship of fire; and difficult enough is Grammar, but the Samans are worst of all\. कष्टानि वनानि 'impervious forests'. कष्टाः पर्वताः ॥ When not having these senses, we have कषितं सुवर्णम् ॥,