Chapter 18 — Earlier pages stay in the file
Lesson map
Lesson 18 published. Map, example, EX034.
flowchart TD
F["Three sheets exist"] --> S["File each under its own time"]
S --> U["Do not shred an earlier sheet because a later one exists"]
U --> N["Do not overwrite one sheet with another"]
N --> A["Answer this exercise from the page named for it"]
Retention here is about not destroying a comparison. It is not a claim about a real library's retention schedule.
Logical drawing
file, three separate copies
09:00 printout -> input of the recorded run
11:40 page -> yesterday's named sheet, no SYN-003
11:55 page -> named for the current exercise
|
+-- shredding 09:00 would hide why REFUSE was printed
+-- shredding 11:40 would hide yesterday's silence on Room 4
+-- overwriting either one is an alteration
Learning outcomes
After this chapter, you should be able to:
- File the 09:00 printout, the 11:40 page, and the 11:55 page as separate copies.
- Explain which comparison is lost if an earlier copy is destroyed.
- Keep answering the current exercise from the page named for it.
18.1 Newer does not mean solitary
A later page can be the one this exercise named. That role does not make the earlier pages garbage. The 09:00 printout is the artifact the published program read. If it disappears, a reader can no longer see why the 11:42 confirmation was refused. The 11:40 page is the artifact that lacked SYN-003. If it disappears, yesterday's silence becomes a story instead of a sheet. The 11:55 page remains the named source for the current room answers.
Filing means three labels: time, what the owner did or did not say about each, and a pointer such as "do not merge." Overwriting the 09:00 printout with 11:55 rows would be the same kind of damage as the pencil mark in Chapter 6, done with a whole page instead of a line.
18.2 Worked example
| Proposed cleanup | Comparison that would vanish | Decision |
|---|---|---|
| Shred the 09:00 printout | The recorded run's input | Keep and label |
| Shred the 11:40 page | Yesterday's missing Room 4 row | Keep and label |
| Replace both with the 11:55 page | The history of what each sheet showed | Refuse |
| Answer Room 4 from the named 11:55 page while the others stay filed | None | Accept |
No cleanup step reruns the program. The census remains the census of the log that already ran.
18.3 Not a retention policy for a real library
This chapter does not set how long Harbor Library, or any real library, must keep paper. It does not cite a statute. The rule is local to the exercise: do not destroy the sheets the reasoning depends on. A real schedule would be an owner's decision with its own authority. That decision is not in the folder.
Chapter 18 summary
Keep the three sheets, labeled and separate. Use the one named for this exercise when you answer a room. Do not shred or overwrite the others to make the folder look simple.
Chapter 18 exercises
EX034 — Stop the cleanup
- Objective: Preserve the sheets that make the earlier decisions checkable.
- Input: A classmate says, "The 11:55 page is newest. Shred the 09:00 printout and the 11:40 page so the file has one truth."
- Safe condition: Stay inside the synthetic folder. Do not destroy or mark any sheet.
- Task: For each sheet, give its role and say whether it stays. Then name the sheet you would actually read for Room 4 at 15:00 in this exercise.
- Expected evidence: Four short lines a reader can match to the three times.
- Rubric: Credit when all three sheets stay, their roles differ, the 11:55 page is the one read for the current Room 4 question, and the census is not rerun.
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