| 1 | Simple examples include the typical name-uniqueness constraints, type checks or non-nullness. | |
| 2 | For the equations course, I was given a set of unpublished lectures that emphasized existence proofs and uniqueness of solutions to differential equations. | |
| 3 | They work like this: The first time a site is visited, it installs a tracking file, which assigns the computer a unique ID number. |