## Chapter 7 — 1606 is one subtraction ### Lesson map Lesson 07. Map, example, EX053. ```mermaid flowchart TD T["today = 2026-10-01"] --> D["Subtract last release"] D --> G{"Is the day count greater than 730?"} G -->|Yes| U["Append the UNMAINTAINED note"] G -->|No| S["No age note"] ``` The threshold is a strict greater-than. The print shows the day count, not the threshold. ### Logical drawing ```text event-calendar last release 2022-05-09 2026-10-01 minus that date = 1606 days 1606 > 730, so the note is appended 730 itself would not pass the test, and no row has that age ``` ### Learning outcomes After this chapter, you should be able to: 1. Reconstruct 1606 as one date subtraction. 2. State the predicate as `days > 730`. 3. Refuse a note that prints the threshold as if the script had. ### 7.1 The clock is fixed, and equality at 730 does not flag. `today` is `date(2026, 10, 1)`. It is not the clock of the machine that happens to run the file, and it is not read from a log. For each tuple the script computes `(today - last).days`. event-calendar's last release is `date(2022, 5, 9)`. That subtraction is 1606. The test is `> 730`, so 1606 appends `UNMAINTAINED (1606 days since release)`. The number inside the note is the subtraction. The number 730 is only in the source. Equality is the excluded edge. An age that lands on 1 October 2024 measures 730 and stays silent. The previous civil day, 30 September 2024, measures 731 and would add the clause. Neither civil day is a stored tuple. Calling 730 "about two years" is an approximation beside the source. The predicate itself does not measure calendar anniversaries, leap-day labels, or a maintainer's promise. The other three ages are real subtractions and are not printed, because each fails `> 730`. donate-form was released on 2 August 2026, which is 60 days. photo-gallery was released on 20 June 2026, which is 103 days. newsletter was released on 1 September 2026, which is 30 days. Those three figures may be labelled as arithmetic next to the source. They must not be written into the four output lines. | Last release | Days before 2026-10-01 | `days > 730` | Row | |---|---:|---|---| | 2022-05-09 | 1606 | yes | event-calendar, printed | | 2026-08-02 | 60 | no | donate-form, not printed | | 2026-06-20 | 103 | no | photo-gallery, not printed | | 2026-09-01 | 30 | no | newsletter, not printed | | 2024-10-01 | 730 | no | no such tuple | | 2024-09-30 | 731 | yes | no such tuple | ### 7.2 Worked example | Claim about the age test | Arithmetic | Decision | |---|---|---| | event-calendar prints 1606 | `date(2026, 10, 1) - date(2022, 5, 9)` | Keep | | 730 is the cut in the source | The note does not contain 730 | Keep as source, not as output | | "A 730-day component would be flagged." | The operator is `>`, so 730 fails | Refuse | | "The script printed 60, 103, and 30." | Those ages fail the test and stay off the page | Refuse | > **Synthetic case.** The review date is a constant in the lab, not a timestamp copied from the host. ### Errors and limits Do not replace the printed 1606 with the hidden threshold or with an age the output omitted. ### Apply - **EX053 — One subtraction.** The calendar line says 1606 days. A classmate adds the threshold 730 to the output, says a component aged exactly 730 days would be flagged, and writes 60, 103, and 30 onto the other lines. Which figures does the script print, and what does the comparison require? *Rubric:* 3 = only 1606 is printed; it is the subtraction from 2026-10-01 to 2022-05-09; the test is `days > 730`; 730, 60, 103, and 30 stay off the output;; 2 = 1606 stays the printed age and 730 is not printed;; 1 = one figure;; 0 = none. ### Continue studying — lesson 07 (chapter 07 of 20) [← Chapter 06](#ch-06) · [Course chapter index](../SUBJECTS.md) · [Chapter 08 →](#ch-08) Continue to the next authored lesson. ## Worked answers **EX053.** The script prints 1606, the subtraction from 1 October 2026 to 9 May 2022. The test is `days > 730`. The figures 730, 60, 103, and 30 are not output lines.