Index - O
| odd | Universum.Base, Universum |
| on | Universum.Function, Universum |
| OnDecodeError | Universum.String.Reexport, Universum.String, Universum |
| One | Universum.Container.Class, Universum.Container, Universum |
| one | Universum.Container.Class, Universum.Container, Universum |
| OneItem | Universum.Container.Class, Universum.Container, Universum.Container, Universum, Universum |
| OnError | Universum.String.Reexport, Universum.String, Universum |
| onException | Universum.Exception, Universum |
| openFile | Universum.Lifted.File, Universum.Lifted, Universum |
| optional | Universum.Applicative, Universum |
| or | Universum.Container.Class, Universum.Container, Universum |
| Ord | Universum.Base, Universum |
| ord | Universum.Base, Universum |
| Ordering | Universum.Base, Universum |
| ordNub | Universum.Nub, Universum |
| orM | Universum.Monad.Container, Universum.Monad, Universum |
| otherwise | Universum.Bool.Reexport, Universum.Bool, Universum |
| over | Universum |
| overflowError | Universum.Base, Universum |