Karnatakabhashabhushana 8.12

udu and uvu [are the substitutes] of the third person in the neuter.

In the scope of the neuter gender, these two substitutes, udu and uvu, occur respectively for the singular and the plural of the third person:

ādudu (‘it became’);

āduvu (‘they became’);

ādapudu (‘it becomes’);

ādapuvu (‘they become’);

appudu (‘it will become’);

appuvu (‘they will become’);

pōdudu (‘it went’);

pōduvu (‘they went’);

pōdapudu (‘it goes’);

pōdapuvu (‘they go’);

pōpudu (‘it will go’);

pōpuvu (‘they will go’).