What does it mean?...It is well known that every technician earns his money not in vain so it’s impossible to replace any technician by any combination of other technicians...
So is such test correct?
4
1 2 3 -1
2 3 4 -1
2 3 -1
1 2 3 4 -1

Certainly NOT!

You can fire the last technician (-:
The first three working altogether will do his work.