UNIT-LENGTH-JOB denotes a job whose length is the same.
(<=> (Unit-Length-Job-Class ?Class)
(And (Fixed-Length-Job-Class ?Class)
(Value-Cardinality ?Class Job-Unit-Length 1)
(Forall (?I)
(=> (Instance-Of ?I ?Class)
(= (Fixed-Length-Job.Length ?I)
(Job-Unit-Length ?Class))))))