Fix abs_finite_series_le signature and add Exercise 7.1.6/7.1.7 state…#448
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teorth merged 1 commit intoteorth:mainfrom Feb 19, 2026
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Fix abs_finite_series_le signature and add Exercise 7.1.6/7.1.7 state…#448teorth merged 1 commit intoteorth:mainfrom
teorth merged 1 commit intoteorth:mainfrom
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rkirov
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Feb 15, 2026
| theorem sum_union_disjoint {X S : Type*} [Fintype X] [Fintype S] | ||
| (E : X → Finset S) | ||
| (disj : ∀ i j : X, i ≠ j → Disjoint (E i) (E j)) | ||
| (cover : ∀ s : S, ∃ i, s ∈ E i) |
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There were a few different ways to write this in type theory, e.g. using explicit call to Finset.biUnion. Let me know if another one is preferred. I thought this one is the cleanest.
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I ended up writing a whole blog post based on this https://rkirov.github.io/posts/sets-vs-types/
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the mathlib version is here https://leanprover-community.github.io/mathlib4_docs/Mathlib/Algebra/BigOperators/Group/Finset/Basic.html#Finset.sum_biUnion but it strikes me as unnecessarily general for the purposes of this book.
…ments - Remove unused (c:ℝ) parameter from abs_finite_series_le - Fix whitespace in finite_series_const_mul and abs_finite_series_le - Add Exercise 7.1.6 (sum over disjoint partition) with Fin n index - Add Exercise 7.1.7 (column-row counting identity) with Fin types Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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