TheoremBase

Differences, Quotients and Absolute Values of Real Numbers, Read in the Type Real

The set-level difference, quotient and absolute value of real numbers lie in the reals and agree with the corresponding terms of the type Real, with their basic value forms.

Statement

In the setting of The Real Numbers, with the Natural Numbers, Integers and Rationals Identified with Subsets of the Reals, and Completeness, let xx and yy be real numbers, read as elements of the type Real\mathrm{Real} of The Real Numbers as a Type (i) where a type is required, with 00, ++, ⋅\cdot, −- and ≤\le those of Real\mathrm{Real} as in The Real Numbers as a Type (ii) and The Real Numbers as a Type (iii), and << the strict relation of ≤\le.

The difference x−yx-y lies in R\mathbb{R} and equals x+(−y)x+(-y), the difference of xx and yy in Real\mathrm{Real}.

If y≠0y\neq0, then the quotient x/yx/y lies in R\mathbb{R}, so it is an element of Real\mathrm{Real}, and equals x⋅y−1x\cdot y^{-1}, where y−1y^{-1} is the reciprocal of yy, and (x/y)⋅y=x(x/y)\cdot y=x.

The absolute value ∣x∣|x| lies in R\mathbb{R}; ∣x∣=x|x|=x if 0≤x0\le x, and ∣x∣=−x|x|=-x if x<0x<0; 0≤∣x∣0\le|x|; and ∣x−y∣=∣y−x∣|x-y|=|y-x|.

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