The s is elided after the augment iṭ if after this s the augment īṭ follows.,
Thus the Aorist-stem of लू is अलाविस् 3.1.44; 7.2.35, the Personal ending त् gets the augment ईट् by 7.3.96; and by the present sutra , this स् between इ and ई is dropped, and we have अलावीत्; so also अदावीत्, असेवीत्, अकोषीत्, अमोषीत् ॥
Why do we say 'after the augment इट्'? Observe अकार्षीत्, अहार्षीत् ॥ Why when the augment ईट् follows ? Observe अलाविष्टाम् अलाविषुः ॥,