TheoremBase

Kit for def:series-nbg

Partial sums, the sequence of absolute values, convergence, divergence and absolute convergence of series of real numbers are predicative conditions, and the sequences whose series converge, diverge or converge absolutely form classes.

Statement

In the setting of Routine Facts, Continued: Typed Arithmetic, Maps and Predicativity, let nβ‰₯1n\ge1 be a metatheoretic number, let x0,…,xnβˆ’1x_{0},\dots,x_{n-1} be distinct set variables, and let i,j<ni,j<n, not necessarily distinct. A condition on x0,…,xnβˆ’1x_{0},\dots,x_{n-1} is predicative if it is expressed by a predicative formula, with x0,…,xnβˆ’1x_{0},\dots,x_{n-1} in place of the variables x1,…,xkx_{1},\dots,x_{k} of Conditions Expressed by a Predicative Formula, and Guards (i) and no displayed variables; N\mathbb{N}, R\mathbb{R}, the operations ++ and β‹…\cdot, the order ≀\le, the strict order << and the elements 00 and 11 of R\mathbb{R}, the distance dRd_{\mathbb{R}} on R\mathbb{R}, the addition of N0\mathbb{N}_{0} and the element 11 of N\mathbb{N} are parameters. Sequences are as in Sequences (i), ∣x∣|x| is the absolute value of x∈Rx\in\mathbb{R}, and the sequence of partial sums, convergence and divergence of a series, and absolute convergence are as in Series of Real Numbers: Partial Sums, Convergence, the Sum and Absolute Convergence (i), Series of Real Numbers: Partial Sums, Convergence, the Sum and Absolute Convergence (ii) and Series of Real Numbers: Partial Sums, Convergence, the Sum and Absolute Convergence (iii).

Partial sums. The condition "xix_{i} and xjx_{j} are sequences in R\mathbb{R}, and xjx_{j} is the sequence of partial sums of xix_{i}" on x0,…,xnβˆ’1x_{0},\dots,x_{n-1} is predicative.

Absolute values. The condition "xix_{i} and xjx_{j} are sequences in R\mathbb{R}, and xj(k)=∣xi(k)∣x_{j}(k)=|x_{i}(k)| for every k∈Nk\in\mathbb{N}" on x0,…,xnβˆ’1x_{0},\dots,x_{n-1} is predicative.

Convergent series. The condition "xix_{i} is a sequence in R\mathbb{R} and its series converges" on x0,…,xnβˆ’1x_{0},\dots,x_{n-1} is predicative.

Divergent series. The condition "xix_{i} is a sequence in R\mathbb{R} and its series diverges" on x0,…,xnβˆ’1x_{0},\dots,x_{n-1} is predicative.

Absolutely convergent series. The condition "xix_{i} is a sequence in R\mathbb{R} and its series converges absolutely" on x0,…,xnβˆ’1x_{0},\dots,x_{n-1} is predicative.

The class of convergent series. There is a class CC such that, for every class aa, a∈Ca\in C if and only if aa is a sequence in R\mathbb{R} whose series converges.

The class of divergent series. There is a class DD such that, for every class aa, a∈Da\in D if and only if aa is a sequence in R\mathbb{R} whose series diverges.

The class of absolutely convergent series. There is a class AA such that, for every class aa, a∈Aa\in A if and only if aa is a sequence in R\mathbb{R} whose series converges absolutely.

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