The affix astāti (astāt) comes after the words of 'direction', 'locality' or 'time' ending in the Locative -7th case, Ablative -5th case, Nominative 1st-Case, without a change of sense.,
The word दिक् शब्दाः means 'words denoting directions'. Thus पुरस्तात्, has all these three significations in the following sentences, पुरस्तादवसति 'he lives eastward'. पुरस्तादागतः 'he came from east' पुरस्ताद् रमणीयम् 'It was delightful previously'. Similarly with अधस्तात् ॥
Why do we say 'after words of direction'? Observe ऐन्द्र्यां दिशि वसति ॥ Why do we say 'ending in the locative, ablative and nominative'? Observe पूर्वम् ग्रामं गतः ॥ Why do we say when the sense is 'a direction', 'a locality' or 'a time'? Observe पूर्वस्मिन् गुरौ वसति 'he lives in the presence of the guru'.
This affix is a स्वार्थिक affix, like the affixes taught previously. The words denoting direction must be primitive words of direction; and not derivative words like ऐन्द्री &c. which also denote direction. The rule of यथासंख्य does not apply here.,