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Reference.org
Isometry
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<p>In mathematics, an isometry (or congruence, or congruent transformation) is a <a href="/facts/Distance/hbXlaEFk">distance</a>-preserving transformation between <a href="/facts/Metric_space/gnBBRXtc">metric spaces</a>, usually assumed to be <a href="/facts/Bijection/j4gTuTmW">bijective</a>. The word isometry is derived from the <a href="/facts/Ancient_Greek/LIK7NlUh">Ancient Greek</a>: ἴσος <i>isos</i> meaning "equal", and μέτρον <i>metron</i> meaning "measure". If the transformation is from a metric space to itself, it is a kind of <a href="/facts/Geometric_transformation/qRjrasJf">geometric transformation</a> known as a <a href="/facts/Motion_(geometry)/x5zUzg7l">motion</a>. </p>