In the sense of 'hard and difficult' or 'light and easy' the affix khal is added to a verb when īṣad and dur and su are combined with it as upapada-s.,
The anuvritti of the phrase 'when related as instrument or location' ceases with this aphorism. The word कृच्छ्र means heavy, and दुर् has the force of conveying that sense. The word अकृच्छ्र means 'light, easy'; and the words ईषत् and सु convey that sense. Thus ईषत्करो भवता कटः 'a mat is made easily by you'; so also दुष्करः 'made with difficulty'; सुकरः 'made with ease'. Similarly ईषद्भोजः 'eating pleasantly'; दुर्भोजः and सुभोजः ।
Why do we say 'after ईषत् &c'.? See कृच्छ्रेण कार्यः कटः 'the mat which is made with difficulty'.
Why do we say 'when meaning 'hard or light'? Observe ईषत्कार्यं 'a small work'.
Of the affix खल्, the letter ख and ल् are indicatory; ख causing the insertion of a nasal (technically called मुम् augment, 6.3.67); and ल् regulates the accent 6.1.196. The augment मुम् will be added in the subsequent sutra, the ख thus having no work in this sutra.,