The four kinds of finding
The check sorts every finding into four kinds. Only the first kind proves that FET cannot build the timetable.
Most checking tools sort their findings by how serious they feel. This one sorts them by what it can prove. The report shows four kinds, always in this order.
Each kind is a tab with its own count. A kind that found nothing has no tab, so you will not see an empty one.
Proven impossible
On screen: Arithmetic, not a guess.
The check reaches every finding here by counting. It compares committed hours against free slots. It reduces the legal start times of an activity to none. It finds two activities that must run at the same time and share a teacher.
You can act on these findings without checking them yourself. If the report says an activity has no legal start time, the solver cannot find one either.
This is the contract of the tool. The check never reports a finding here that it cannot prove. A tool that raises one false alarm is a tool you stop believing.
Mistakes
On screen: Something here is probably not what you meant.
These findings do not stop a solve. They show that your rules say something you probably did not intend.
- A rule points at something that no longer exists.
- A rule targets an activity that you switched off.
- Two rules say exactly the same thing.
- A soft preference can never apply, so FET ignores it.
None of these makes a timetable impossible. Rules that nobody understands cause next term's mystery.
What makes this file hard
On screen: This is not a problem. It is the work the solver must do.
Nothing here is wrong. This kind describes the pressure in your file. It names the activities that have almost no room left. It names the parts of the week that are tight.
⚠ Read this kind before you make the week tighter.
The heading changes for a solved file. It then reads What made this file hard, because the work is complete.
What ran on this file
On screen: Rule types we list and count, never judge.
This kind is quiet, and it reports on the check itself rather than on your file. It lists the rule types it counted. It tells you when your solver mode stops a check from running. It tells you when the check stopped early on a very large file.
Read this kind when the report looks emptier than you expected. It usually explains why.
A missing tab is not a guarantee
The check reports what it can prove. It does not follow that everything else is correct.
No "Proven impossible" tab means "nothing was proven impossible". It does not mean "this will solve".
⚠ This is the most important sentence on the page, and the screen makes it easy to miss: the tab is simply absent, so there is nothing to read and nothing to click. Absence is the good outcome, not the complete one.
A timetable can be possible in arithmetic and still take FET a long time. It can still need rules relaxed before it lands. See What it cannot tell you.