The connection between praṇava  and sohaṃ (continuation)

Besides the Nādabindūpaniṣad, I came across other interpretations of how praṇava is manifested from mantra sohaṃ. There is also the interpretation in which, if we remove ‘sa’ and ‘ha’ from sohaṃ, we get praṇava Oṃ. One of the early texts that I went through was the Prapañcasāra Tantra (4.21):

सकारं च हकारं च लोपयित्वा प्रयोजयेत्।संधिं वै पूर्वरूपाख्यं ततोऽसौ प्रणवो भवेत्।।४.२१ ।।

sakāraṃ ca hakāraṃ ca lopayitvā prayojayet ।
saṃdhiṃ vai pūrvarūpākhyaṃ tato’sau praṇavo bhavet ।।4.21।।

According to the image of pūrva rūpa saṃdhi, removing ‘sa’ and ‘ha’, one must definitely get that praṇava (oṃ) from there.

Explanation: pūrva rūpa saṃdhi is connected with the ending ओ/o, which stands before अ/a of the next word, turning into a sign known as avagraha / ऽ. Thus, the text implies that from ओ/o we get the praṇava mantra.

Oṃkāra inside sohaṃ

Many connections can be found between the praṇava oṃ and the mantrahaṃsa” (sohaṃ). The symbol of the swan, like a bird, is found in the Nādabindūpaniṣad. This image and the connection with praṇava are described there as following:

अकारो दक्षिणः पक्ष उकारस्तूत्तरः स्मृतः।
मकारं पुच्छमित्याहुरर्धमात्रा तु मस्तकम् मस्तकम् १॥

akāro dakṣiṇaḥ pakṣa ukārastūttaraḥ smṛtaḥ
makāraṃ pucchamityāhurardhamātrā tu mastakam mastakam 1

It is believed (smṛtaḥ) the mātrā “A” (akāraḥ) is in the right wing (dakṣinaḥ-pakṣaḥ), the mātrā “U”(ukāraḥ) in the north (uttaraḥ – “north” is “in the left” wing). Thus (iti), in his tail (puccham) is the mātrā “Ma” (makāraṃ), also (tu) they say (āhuḥ), ia half the mātrā, (ardhamātrā) is in his head (mastakam), i.e. nasalized vibration.