deriv LSK ETT STT aSTA ALPH OLDHOMEPAGE NEWHOMEPAGE

@joining table for V before V

padafinal a अ

(a अ A आ) plus (i इ I ई) makes e ए by AdguNaH

(a अ A आ) plus (u उ U ऊ) makes o ओ by AdguNaH

(a अ A आ) plus (R ऋ RR ॠ L ऌ) makes ar अर् ar अर् al अल् by AdguNaH and uraNraparaH

(a अ A आ) plus (e ए ai ऐ) makes ai ऐ by vRddhireci

(a अ A आ) plus (o ओ au औ) makes au औ by vRddhireci

savarNa vowels

(a अ A आ) plus (a अ A आ) makes I ई by akassavarN...

(i इ I ई) plus (i इ I ई) makes I ई by akassavarN...

(u उ U ऊ) plus (u उ U ऊ) makes U ऊ by akassavarN...

(R ऋ RR ॠ L ऌ) plus (R ऋ RR ॠ L ऌ) makes RR ॠ by akassavarN...

padafinal i इ I ई u उ U ऊ R ऋ RR ॠ L ऌ

When the /ik are before a non-savarNa, they change like this, by ikoyaNaci —

i इ I ई → y य्
u उ U ऊ → v व्
R ऋ RR ॠ → r र्
L ऌ → l ल्

/ec letters

e ए + a अ → e ' ए ऽ by eGaHpadAnt...
o ओ + a अ → o ' ओ ऽ by eGaHpadAnt...

e ए o ओ before the other vowels, and ai ऐ au औ before all vowels, change like this —

e ए → a:: अ‌ by ecoyavAyAvaH and lopazzAkaly...
o ओ → a:: अ‌ by ecoyavAyAvaH and lopazzAkaly...
ai ऐ → A:: आ‌ by ecoyavAyAvaH and lopazzAkaly...
au औ → Av आव् by ecoyavAyAvaH (no lopazzAkaly... this time)

That lopazzAkaly... is an optional rule. Does /pANini teach that we have to apply it after e ए o ओ ai ऐ but not after au औ?

No, /pANini does not teach that. Doing that is just a modern custom.

In very old texts you may sometimes hear the other options, like —

he viSNav ity abravIt हे विष्णवित्यब्रवीत्
he said "he viSNo हे विष्णो"