For three months Nerva ruled jointly with Trajan (Aur.
His son, BoccHus, was king of Mauretania, jointly with a younger brother Bogud.
At Vienna, from 1452, he was the pupil and associate of George Purbach (1423-1461), and they jointly undertook a reform of astronomy rendered necessary by the errors they detected in the Alphonsine Tables.
There were some decisions that should be made jointly, and being in control meant taking full responsibility.
The landlord lets his land to two or more persons jointly, who undertake to restore it to him in good condition with one-third of it interrozzito, that is, fallow, so as to be cultivated the following year according to triennial rotation.