fix: disambiguate duplicate Verso labels in Section 5.3

[Chessing234]

Section 5.3 has five groups of declarations sharing one docstring:

• Proposition 5.3.3 / Exercise 5.3.1 — 2
• Definition 5.3.1 (Real numbers) — 2
• Definition 5.3.4 (Addition of reals) — 2
• Proposition 5.3.11 (laws of algebra) — 4 instances
• Examples 5.3.13 — 5 examples

Definitions and propositions fold the part into the parenthetical (as in #624); the five examples take part letters (as in #634 for Examples 5.2.2). Docstrings only.

Checked: no duplicate one-line docstrings remain in the file, all edited lines within 100 characters.

lake build Analysis.Section_5_3 succeeds locally — ✔ [3268/3268] Built Analysis.Section_5_3 (103s), Build completed successfully.

[teorth]

Thanks — most of this is exactly right, and I've merged the sibling PRs (#651, #653, #655, #656, #657, #659, #660, #661) that use the same descriptive style.

One change here I'd like adjusted before merging. The Examples 5.3.13 block is prose in the text, not an enumerated list — ch5 reads:

The sequence $1$, $-1$, $1$, $-1$, ... is bounded away from zero (all the coefficients have absolute value at least 1). But the sequence $0.1, 0.01, 0.001, \dots$ is not bounded away from zero, and neither is $0, 0.9, 0.99, 0.999, \dots$. The sequence $10, 100, 1000, \dots$ is bounded away from zero, but is not bounded.

So there are no parts (a)–(e) to refer to; adding them makes the docstring claim a structure the book doesn't have, and a reader who goes looking for "Examples 5.3.13(c)" won't find it. Could you use the same descriptive parentheticals you've used everywhere else in this PR? Something like:

• Examples 5.3.13 (alternating signs)
• Examples 5.3.13 (decaying powers of ten)
• Examples 5.3.13 (approaching one from below)
• Examples 5.3.13 (growing powers of ten, bounded away from zero)
• Examples 5.3.13 (growing powers of ten, not bounded)

Everything else in the PR is good to go as-is.

[Chessing234]

Done in 0248c0d — the five Examples 5.3.13 labels now use your suggested parentheticals: (alternating signs), (decaying powers of ten), (approaching one from below), (growing powers of ten, bounded away from zero), (growing powers of ten, not bounded). Nothing else changed.