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))))))