काशिका वृत्ति (आचार्य वामन एवं जयादित्य - अष्टाध्यायी सूत्र-वृत्ति सम्पूर्ण सान्वय सटीक)

सार्वधातुकयोर्दीर्घः" - it doesn't double there.
Wait, let's look at "पित्र्यम्" vs "पित्रियम्" vs "पित्रीयम्":
Wait, why does L24 say "पितुरागतं पित्र्यम्"?
Wait! Let's search the grammar rule:
Is there a vārtika or something?
Wait! In Ashtadhyayi:
"ऋत इद्धातोः" (7.1.100)
"रीङ् ऋतः" (7.4.27)
Wait! Under 7.4.27:
Does Kashika say:
"क्ङितीत्येतन्निवृत्तम्, तेनेहापि भवति — पितुरागतं पित्र्यम्"?
Wait, why would "पितुरागतं पित्र्यम्" be an example of रीङ्?
Wait, if it were an example of रीङ्, पितृ + यत् would become *पित्रीयम्!
Wait, could it be: "तेनेह न भवति"? No, "तेनेहापि भवति"!
Wait, DOES Kashika have this?
Wait! What if it says "पित्र्यम्" in some editions?
Wait, let's search Google mentally for:
"क्ङितीत्येतन्निवृत्तं" "पितुरागतं"
Wait! Could it be: "पितुर्यत्" (4.2.100) -> प