A claim needs a witness. These six levels are how ChuuInstruct talks about proof. Only the top one earns the word “works.”
| Tier | Means |
|---|---|
| T0 | Written. Not run. |
| T1 | Parses. |
| T2 | Compiles. |
| T3 | Tests pass. |
| T4 | Runs in a real process on the real machine. |
| T5 | The surface that matters was observed — a window, a page, a file that actually appeared. |
Passing tests (T3) is not the same as the program looking right (T5). Say which tier you reached, and say what you did not check.