सोपानम् १७: अङ्ग-कार्यम् & गुण-वृद्धि-संविधानम् (Stem Processing Engine)
Sopāna 17: Mastering how roots mutate into the universal Adanta stem (अदन्ताङ्गम्) via Guṇa strengthening (सार्वधातुकार्धधातुकयोः ७.३.८४) vs. the Ṅit firewall (क्ङिति च १.१.५)
१. दर्शनम् — अङ्ग-निर्माण-रहस्यम् (The Two-Rule Guṇa Toggle Switch)
"सार्वधातुकार्धधातुकयोः। क्ङिति च॥"
— अष्टाध्यायी (७.३.८४ & १.१.५)
Before Sārvadhātuka endings, the root vowel strengthens to Guṇa: इ/ई ➔ ए, उ/ऊ ➔ ओ, ऋ ➔ अर्. This turns √भू into भो + अ ➔ भव- and √नी into ने + अ ➔ नय-!
Whenever an affix is Ṅidvat (like 'श' in 6th Gaṇa Tudādi), sūtra 1.1.5 erects a complete firewall: Guṇa is strictly forbidden! That is why √लिख् produces लिखति (never *लेखति) and √तुद् produces तुदति.
Once this step completes, all 4 Adanta Gaṇas produce finished stems ending in short '-a' (भव-, नृत्य-, लिख-, चोरय-). Downstream conjugation across all 4 Lakāras now becomes completely standardized!