A four-task schedule with complete constraints
A fictional office schedules four distinct tasks A, B, C and D into four numbered slots, one task in each slot. Task A must occur immediately before B. Task D is fixed in slot 4. Task C has no additional restriction. A trainee proposes arranging C,A,B,D and another proposes A,C,B,D. The office asks which arrangements are feasible and whether the first task is determined uniquely. There are no parallel tasks, no unused slots and no unmentioned precedence relationships. The rules are supplied for this reasoning exercise and do not describe an operational protection procedure. Evaluate each full arrangement against every rule, keeping the meaning of immediately before distinct from the looser statement that one task simply occurs sometime earlier.
1. Which proposed arrangement is feasible?
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C,A,B,D is feasible: A and B occupy adjacent slots 2 and 3, and D is in slot 4. A,C,B,D fails immediate precedence because C separates A from B.
2. Is the first task fixed?
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No. A,B,C,D is also feasible. Thus either A or C can occur first under the stated rules.
3. Can B occupy the first slot?
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No. B requires A immediately before it, and there is no earlier slot before slot 1.