@examples of pac plus pit liT

pac पच् reduplicates to **papac- पपच् before all /liT endings. But actually this **papac- पपच् stays only if the /liT is /pit, namely, if it is /Nal or /thal. With /Nal —

**papac- पपच् + /liT /tip OR /mip
→ papac- पपच् + /Nal
→ papAc- पपाच् + /Nal with /vRddhi by ata::upadh...
→ **papAca पपाच "he / she / I cooked"

In the case of /mip, the /vRddhi is optional —

**papac- पपच् + /mip → **papaca पपच "I cooked" optionally by NaluttamovA

With /thal —

pac पच् + /liT /sip
→ pac पच् + /thal
→ **papac- पपच् + /thal, with no /iT because of optional RtobhAradv...
(thal थल् does not trigger thalicaseTi coz it's /iT-less)
→ papak- पपक् + /thal by coHkuH
→ !**papaktha पपक्थ "you' cooked"

However if we don't take the RtobhAradv... option, then rule thalicaseTi makes **pec- पेच् —

pac पच् + ithal इथल् → **pecitha पेचिथ