TheoremBase

Predicative Formulas for Bijections from a Segment [n] and for Increasing Listings

The conditions that f is a bijection from a segment [n] of the natural numbers onto B, and that x is such a bijection with strictly increasing real values, are expressed by predicative formulas.

Statement

In the setting of The Real Line: Standing Notation and Background for Calculus on Intervals, with predicative meant for formulas with abbreviations, conditions expressed by a predicative formula are as in Conditions Expressed by a Predicative Formula, and Guards (ii), with parameters and their fixed values as in Conditions Expressed by a Predicative Formula, and Guards (i); (i) and (ii) are statements of the metatheory. For n∈N0n\in\mathbb{N}_{0}, [n][n] is as in Intervals of Natural Numbers (ii); bijections are as in Injective, Surjective and Bijective Functions between Classes (iii), and x(i)x(i) is the value of a map xx at a point ii of its domain. The letters ff, xx, nn and BB are distinct set variables, and N0\mathbb{N}_{0}, N\mathbb{N}, the order ≤\le of N0\mathbb{N}_{0} and the strict order << of R\mathbb{R} are parameters. For i,j∈N0i,j\in\mathbb{N}_{0}, i<ji<j refers to the strict order of N0\mathbb{N}_{0}, as in The Natural Numbers and the Natural Numbers with Zero: Arithmetic, Order, Induction and Recursion (v); and x(i)<x(j)x(i)<x(j) means that the ordered pair (x(i),x(j))(x(i),x(j)) lies in the strict order << of R\mathbb{R}.

The condition "n∈N0n\in\mathbb{N}_{0} and ff is a bijection from [n][n] onto BB" on ff, nn and BB is expressed by a predicative formula.

The condition "n∈N0n\in\mathbb{N}_{0}, xx is a bijection from [n][n] onto BB, and x(i)<x(j)x(i)<x(j) for all i,j∈[n]i,j\in[n] with i<ji<j" on xx, nn and BB is expressed by a predicative formula.

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