सदेवेदं सर्वं जगदवगतं वाङ्मनसयोः
सतोऽन्यन्नास्त्येव प्रकृतिपरसीम्नि स्थितवतः ।
पृथक्किं मृत्स्नायाः कलशघटकुम्भाद्यवगतं
वदत्येष भ्रान्तस्त्वमहमिति मायामदिरया ॥ ३९२ ॥
392. All this universe cognised by speech and mind is nothing but Brahman; there is nothing besides Brahman which exists beyond the utmost range of Prakriti. Are the pitcher, jug, or jar etc. known to be distinct from the earth of which they are composed? It is the deluded man who talks of "Thou" and "I" as an effect of the wine of Maya.
Commenting on this, the Acharya says:
एतेन सर्वेषां बाध उपादानेन अज्ञानेन सह नाशः उक्तो भवति ।
// Thus, the sublation (negation / destruction) of everything, along with the material cause ajnāna, has been stated. //
He also stated therein: यद्वा प्रकृतेः मूलप्रकृतेः मायायाः परा या सीमा तस्या अपि कल्पनाधिष्ठानं निर्गुणं ब्रह्म ..
//(Or) the ultimate limit of mulaprakriti, māyā, is also superimposed on Nirguna Brahman.//
Shankara, more than once, has said:
प्रकृतिस्थः प्रकृतौ अविद्यालक्षणायां ...
भूतानां प्रकृतिः अविद्यालक्षणा अव्यक्ताख्या...
भूतप्रकृतेः मोक्षणम् अभावगमनं च ये विदुः, प्रकृतिं च यथोक्ताम् अविद्यालक्षणां - all in the BGB 13th chapter. For Shankara, Maya, an insentient power that causes creation, is also avidya (ignorance). He states: By Direct Knowledge, this Prakriti/Avidya is realized to be non-existent. That means its substratum is Nirguna Brahman
From this we conclude that those who accept *mulāvidyā* as the upādāna for samsāra have not stated anywhere that it is a real entity, as real as Brahman, which would not go away and would make Brahman *sadvitīya* (one with a second).
Om Tat Sat
subbu