In the room of idam 'this', in the case of its re-employment in a subsequent member of the same sentence and referring to the same thing (anvādeśa) there is the substitution of aś which is anudātta (gravely accented), when the Instrumental -3rd case-affix and the rest follow.,
The word अन्वादेश means literally saying (adesa) 'after' (anu) or after-say or re-employment.
अश् (actually अ) replaces इदम् in all cases except the nominative and the accusative, when anvadesa or repetition is implied. अश् replaces the whole of इदम् by 55 and not only the final म्. Anvadesa means repeating in a second sentence with reference to the preceding in which it has already been used. Both pronouns, the antecedent and the subsequent, must refer to the same object. As, आभ्याम् छात्राभ्याम् रात्रिरधीता, अथो आभ्यामहरप्यधीम् 'Those students studied in the night and they have read in the day also.' The substitute अश् will replace इदम्, even when the latter takes the affix अकच् (V. 3. 71.)
अस्मै छात्राय कम्बलं देहि, अथो अस्मै शाकटमपि देहि 'Give this student a blanket and give him also a cloth'. अस्य छात्रस्य शोभनं शीलम्, अथो अस्य प्रभूतं स्वम्, 'this student's conduct is excellent, and his wealth is great.'
So also when the affix अकच् 5.3.71 comes after the Pronominal as इमकाभ्यां छात्राभ्यां रात्रिरधीता, अथो आभ्यामहरप्यधीतम्.
The mere mentioning in a subsequent sentences is now anvadesa : it is the employment again of what has been employed to direct one operation, to direct another operation. Therefore the rule does not apply here :- देवदत्तं भोजय, इमंच यज्ञदत्तम् 'feed Devadatta and this Yajnadatta.',