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Viewing Version 3 of 'well-defined'
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Title of object: well-defined
Canonical Name: WellDefined
Type: Definition

Created on: 2007-09-06 06:32:32
Modified on: 2007-09-06 08:56:50

Creator: pahio
Modifier: Algeboy
Author: CWoo
Author: stevecheng
Author: pahio

Classification: msc:00A05
Synonyms: well-defined=well defined

Revision comment (for changes between this and next version):

corrected a typo and added a little on well-defined functions.

Preamble:

% this is the default PlanetMath preamble. as your knowledge
% of TeX increases, you will probably want to edit this, but
% it should be fine as is for beginners.

% almost certainly you want these
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{amsfonts}

% used for TeXing text within eps files
%\usepackage{psfrag}
% need this for including graphics (\includegraphics)
%\usepackage{graphicx}
% for neatly defining theorems and propositions
\usepackage{amsthm}
% making logically defined graphics
%\usepackage{xypic}

% there are many more packages, add them here as you need them

% define commands here

\theoremstyle{definition}
\newtheorem*{thmplain}{Theorem}
Content:

A mathematical concept is {\em well-defined} (German {\em wohldefiniert}, French {\em bien d\'efini}), if its contents in \PMlinkescapetext{independent} on the form or the alternative representative which is used for defining it.

For example, in defining the \PMlinkname{power}{FractionPower} $x^r$ with $x$ a positive real and $r$ a rational number, we can freely choose the fraction form $\frac{m}{n}$ ($m\in\mathbb{Z}$,\, $n\in\mathbb{Z}_+$) of $r$ and take
$$x^r := \sqrt[n]{x^m}$$
and be sure that the value of $x^r$ does not depend on that choice (this is justified in the entry fraction power). So, the $x^r$ is well-defined.