157. Indeclinable active past participles - or gerunds or absolutives,
according to some modern grammarians - are formed with the suffixes
-tvaa, -tvaana, -tuuna, -ya and -tya.

(1) These may be joined to the roots or bases by means of a connecting i.
(2) Sometimes the last consonant of the root is dropped before these.
(3) The final long vowel of a root is sometimes shortened or
strengthened before these.
(4) t of the suffixes is dropped or changed together with the last
consonant of the root in a few cases.

(a) joined to the roots by means of i
pacA + i + tvaa = pacitvaa (having cooked)
karA + i + tvaana = karitvaana (having done)
vandA + i + tuuna = vandituuna (having bowed down)

(i) joined to the bases
bhu~njA + i + tvaa = bhu~njitvaa (having eaten)
sayA + i + tvaana = sayitvaana (having slept)
su.nA + i + tuuna = su.nituuna (having heard)
jahA + i + tvaa = jahitvaa (having abandoned)

(b) where the last consonant is dropped
karA + tvaa = katvaa (having done)
hanA + tvaa = hatvaa (having killed)
bhujA + tvaa = butvaa (having eaten)
padA + tvaa = patvaa (having come or arrived)
cajA + tvaa = catvaa (having abandoned)
chidA + tvaa = chetvaa (having cut or broken)
bhidA + tvaa = bhetvaa (having broken or opened)

(c) final vowel shortened or strengthened
daa + tvaa = datvaa (having given)
nii + tvaa = netvaa (having carried)
huu + tvaa = hutvaa (having been)
~naa + tvaa = ~natvaa (having known)
.thaa + tvaa = .thatvaa (having stood or stayed)

(d) t of suffix is dropped or changed
disa + tvaa = disvaa (having seen)
labha + tvaa = laddhaa (having gotten)

(e) where nothing but the elison of the final vowel of the root has
taken place
hanA + tvaa = hantvaa (having killed)
manA + tvaa = mantvaa (having thought)
nii + tvaa = niitvaa (having carried)
yaa + tvaa = yaatvaa (having gone)
paa + tvaa = paatvaa (having drunk)

In gamU + tvaa = gantvaa (having gone), m is changed to n.

158. -ya is assimilated, in many cases, to the last consonant of the
root; it is directly added to the roots ending in a long vowel.

(1) Directly added:
aa + daa + ya = aadaaya (having taken)
pa + haa + ya = pahaaya (having abandoned)
aa + nii + ya = aaniiya (having brought)
aa + ~naa + ya = a~n~naaya (having known)

(2) Assimilated with the preceding consonant:
aa + gamU + ya = aagamya = aagamma (having come)
ni + sadA + ya = nisadya = nisajja (having sat)