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Predicative Formulas for Differences, Quotients, Absolute Values, Distances and the Strict Order of the Real Numbers, at Any Variable Positions

Membership in the real numbers together with being the difference, quotient, absolute value or distance of given real numbers, and the strict order of the real numbers, are predicative conditions at any variable positions.

Statement

In the setting of Routine Facts Used Without Citation: Arithmetic, Maps, Predicativity and Indices, let n≥1n\ge1 be a metatheoretic number, let x0,…,xn−1x_{0},\dots,x_{n-1} be distinct set variables, and let i,j,k<ni,j,k<n, not necessarily distinct. Each clause states that a condition on x0,…,xn−1x_{0},\dots,x_{n-1} is predicative: expressed by a predicative formula, with x0,…,xn−1x_{0},\dots,x_{n-1} in place of the variables x1,…,xNx_{1},\dots,x_{N} of Conditions Expressed by a Predicative Formula, and Guards (i) and no displayed variables. Here R\mathbb{R}, ≤\le, ++, ⋅\cdot, 00 and 11 are as in The Real Numbers (i), The Real Numbers (iii) and The Real Numbers (iv), and << is the strict order associated with ≤\le.

Differences. "xi∈Rx_{i}\in\mathbb{R}, xj∈Rx_{j}\in\mathbb{R} and xk=xi−xjx_{k}=x_{i}-x_{j}".

Quotients. "xi,xj∈Rx_{i},x_{j}\in\mathbb{R}, xj≠0x_{j}\neq0 and xk=xi/xjx_{k}=x_{i}/x_{j}".

Absolute values. "xi∈Rx_{i}\in\mathbb{R} and xk=∣xi∣x_{k}=|x_{i}|".

Distances. "xi,xj∈Rx_{i},x_{j}\in\mathbb{R} and xk=∣xi−xj∣x_{k}=|x_{i}-x_{j}|".

The strict order. "xi<xjx_{i}<x_{j}".

Positivity. "0<xj0<x_{j}".

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