A valādi ārdhadhātuka affix optionally takes iṭ after kuṣ when it is preceded by nir,
As निष्कोष्टा or निष्कोषिता, निष्कोष्टुम् or निष्कोषितुम्, निष्कोष्टव्यम् or निष्कोषितव्यम् ॥ But only कोषिता, कोषितुं, कोषितव्यम् without निर् ॥ The exhibition of निर् instead of निस् indicates the existence of a separate and distinct preposition निर्, besides निस् ॥ It is the र् of this निर् which is changed to ल् by 8.2.19, in निलयनम्; for the र् of निस् being asiddha could not be changed to ल् ॥,